[clang][Headers] Avoid compiler warnings in builtin headers

[ddcc]

Summary

While debugging module support using -Wsystem-headers, we discovered that if
-Werror, and -Wundef or -Wmacro-redefined are specified, they can cause errors
to be generated in these builtin headers.

[aaron.ballman]

Thanks for catching this! As far as these changes go, they're pretty reasonable, but don't seem like they hit all of the problem areas. There's 20+ occurrences of #if __STDC_VERSION__ and 10+ of #if __cplusplus in lib/Headers; shouldn't they all be updated?

clang/lib/Headers/stdint.h

94–95

It seems to me that a cleaner approach to this is to #undef the macros we expect to be redefining before we redefine them instead of disabling the definition warning entirely. For example, it would still be useful for a user to find out that our stdint.h redefines some symbol from their own header files from an earlier inclusion.

551

Why does this usage not need to be changed?

[ddcc]

Undef macros instead, handle other header files

[tra]

clang/lib/Headers/__clang_cuda_builtin_vars.h

37 ↗

(On Diff #449118)

Are there actual use cases where CUDA headers are used from a non-C++ compilation? I do not think they will compile with non-C++ compilation at all.

I'm curious how we managed to run into a situation where CUDA headers may be used w/o C++.

I think a better fix here and other CUDA headers may be to add

#if !defined(__cplusplus)
#error CUDA headers must be used from a CUDA/C++ compilation.
#endif

[ddcc]

clang/lib/Headers/__clang_cuda_builtin_vars.h

37 ↗

(On Diff #449118)

Sure, I can do that. I'm not familiar with CUDA or its headers, so I previously just updated them all.

[ddcc]

Error out on undef __cplusplus in CUDA headers

[tra]

clang/lib/Headers/__clang_cuda_builtin_vars.h

14 ↗

(On Diff #449403)

Nit: the error message sounds a bit odd.
Perhaps rephrase it as This CUDA header requires C++.

clang/lib/Headers/__clang_hip_cmath.h

381 ↗

(On Diff #449403)

HIP headers are also not expected to compile w/o C++ and we may want a #errorhere, too.

Actually, I'm not even sure if we shopuld/need to add #if defined(__cplusplus)in files that are clearly C++ -- undefined macro warning will be the least of one's worries if they attempt to compile it w/o C++.

Perhaps it would make sense to limit these changes to the headers intended to be used from both C and C++? Both CUDA and HIP are expected to never be included from a non-C++ compilation and will never trigger the undefined macro warning on __cplusplus.

@yaxunl - FYI.

[ddcc]

clang/lib/Headers/__clang_hip_cmath.h

381 ↗

(On Diff #449403)

Sure, I'm fine with leaving those headers alone since I'm not familiar with them.

[ddcc]

Drop changes to CUDA/HIP/OpenMP headers

[iana]

clang/lib/Headers/stdint.h

99–100

What are you seeing that's defining __int_least64_t and all these other ones by the time you get here? It's surprising to me that so much preprocessor state exists when you hit this point considering that this file doesn't include anything else. Is this some kind of artifact with how the OS module map is making a module for stdint.h?

[iana]

clang/lib/Headers/stdint.h

99–100

Oh I see, it's not these ones that are the problem, it's the redefinitions below. I guess it's a bigger change, but I wonder if flipping the order would be cleaner? e.g.

#ifdef __INT32_TYPE__
# define __int_least32_t int32_t
#endif

#ifdef __INT64_TYPE__
# ifndef __int_least32_t
#  define __int_least32_t int64_t
# endif
#endif

I guess it's an extra line per type doing it that way, but maybe it's more obvious? (Maybe I just don't do a lot of preprocessor programming, but #undef feels like a code smell to me)

[ddcc]

clang/lib/Headers/stdint.h

99–100

I'm a little reluctant to change this file too much since it's tedious and error-prone, but yeah if we can agree on a solution, I can go ahead and make the change.

[aaron.ballman]

These changes look reasonable to me, thanks!

clang/lib/Headers/stdint.h

99–100

I'm not toooooo sad about the #undef though this does make preprocessing this file do more work. However, rearranging the macros in this file might be a challenge given how much these macros interact with one another. From the comments just above:

* These macros are defined using the same successive-shrinking approach as
* the type definitions above. It is likewise important that macros are defined
* in order of decending width.

clang/lib/Headers/float.h

 
 /* Undefine anything that we'll be redefining below. */
 #  undef FLT_EVAL_METHOD
 #  undef FLT_ROUNDS
 #  undef FLT_RADIX
 #  undef FLT_MANT_DIG
 #  undef DBL_MANT_DIG
 #  undef LDBL_MANT_DIG
-#  if __STDC_VERSION__ >= 199901L || !defined(__STRICT_ANSI__) ||              \
-      __cplusplus >= 201103L ||                                                \
-      (__STDC_HOSTED__ && defined(_AIX) && defined(_ALL_SOURCE))
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) ||              \
+    !defined(__STRICT_ANSI__) ||                                               \
+    (defined(__cplusplus) && __cplusplus >= 201103L) ||                        \
 #    undef DECIMAL_DIG
 #  endif
 #  undef FLT_DIG
 #  undef DBL_DIG
 #  undef LDBL_DIG
 #  undef FLT_MIN_EXP
 #  undef DBL_MIN_EXP
 #  undef LDBL_MIN_EXP

 #  undef DBL_MAX
 #  undef LDBL_MAX
 #  undef FLT_EPSILON
 #  undef DBL_EPSILON
 #  undef LDBL_EPSILON
 #  undef FLT_MIN
 #  undef DBL_MIN
 #  undef LDBL_MIN
-#  if __STDC_VERSION__ >= 201112L || !defined(__STRICT_ANSI__) ||              \
-      __cplusplus >= 201703L ||                                                \
-      (__STDC_HOSTED__ && defined(_AIX) && defined(_ALL_SOURCE))
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) ||              \
+    !defined(__STRICT_ANSI__) ||                                               \
+    (defined(__cplusplus) && __cplusplus >= 201703L) ||                        \
 #    undef FLT_TRUE_MIN
 #    undef DBL_TRUE_MIN
 #    undef LDBL_TRUE_MIN
 #    undef FLT_DECIMAL_DIG
 #    undef DBL_DECIMAL_DIG
 #    undef LDBL_DECIMAL_DIG
 #    undef FLT_HAS_SUBNORM
 #    undef DBL_HAS_SUBNORM
 #    undef LDBL_HAS_SUBNORM
 #  endif
 #endif
 
 /* Characteristics of floating point types, C99 5.2.4.2.2 */
 
 #define FLT_EVAL_METHOD __FLT_EVAL_METHOD__
 #define FLT_ROUNDS (__builtin_flt_rounds())
 #define FLT_RADIX __FLT_RADIX__
 
 #define FLT_MANT_DIG __FLT_MANT_DIG__
 #define DBL_MANT_DIG __DBL_MANT_DIG__
 #define LDBL_MANT_DIG __LDBL_MANT_DIG__
 
-#if __STDC_VERSION__ >= 199901L || !defined(__STRICT_ANSI__) ||                \
-    __cplusplus >= 201103L ||                                                  \
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) ||              \
+    !defined(__STRICT_ANSI__) ||                                               \
+    (defined(__cplusplus) && __cplusplus >= 201103L) ||                        \
     (__STDC_HOSTED__ && defined(_AIX) && defined(_ALL_SOURCE))
 #  define DECIMAL_DIG __DECIMAL_DIG__
 #endif
 
 #define FLT_DIG __FLT_DIG__
 #define DBL_DIG __DBL_DIG__
 #define LDBL_DIG __LDBL_DIG__
 

 #define FLT_EPSILON __FLT_EPSILON__
 #define DBL_EPSILON __DBL_EPSILON__
 #define LDBL_EPSILON __LDBL_EPSILON__
 
 #define FLT_MIN __FLT_MIN__
 #define DBL_MIN __DBL_MIN__
 #define LDBL_MIN __LDBL_MIN__
 
-#if __STDC_VERSION__ >= 201112L || !defined(__STRICT_ANSI__) ||                \
-    __cplusplus >= 201703L ||                                                  \
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) ||              \
+    !defined(__STRICT_ANSI__) ||                                               \
+    (defined(__cplusplus) && __cplusplus >= 201703L) ||                        \
     (__STDC_HOSTED__ && defined(_AIX) && defined(_ALL_SOURCE))
 #  define FLT_TRUE_MIN __FLT_DENORM_MIN__
 #  define DBL_TRUE_MIN __DBL_DENORM_MIN__
 #  define LDBL_TRUE_MIN __LDBL_DENORM_MIN__
 #  define FLT_DECIMAL_DIG __FLT_DECIMAL_DIG__
 #  define DBL_DECIMAL_DIG __DBL_DECIMAL_DIG__
 #  define LDBL_DECIMAL_DIG __LDBL_DECIMAL_DIG__
 #  define FLT_HAS_SUBNORM __FLT_HAS_DENORM__

clang/lib/Headers/limits.h

 #define MB_LEN_MAX 1
 #endif
 
 #define CHAR_BIT  __CHAR_BIT__
 
 /* C2x 5.2.4.2.1 */
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 #define BOOL_WIDTH   __BOOL_WIDTH__
 #define CHAR_WIDTH   CHAR_BIT
 #define SCHAR_WIDTH  CHAR_BIT
 #define UCHAR_WIDTH  CHAR_BIT
 #define USHRT_WIDTH  __SHRT_WIDTH__
 #define SHRT_WIDTH   __SHRT_WIDTH__
 #define UINT_WIDTH   __INT_WIDTH__
 #define INT_WIDTH    __INT_WIDTH__

 #else
 #define CHAR_MIN SCHAR_MIN
 #define CHAR_MAX __SCHAR_MAX__
 #endif
 
 /* C99 5.2.4.2.1: Added long long.
    C++11 18.3.3.2: same contents as the Standard C Library header <limits.h>.
  */
-#if __STDC_VERSION__ >= 199901L || __cplusplus >= 201103L
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) ||              \
+    (defined(__cplusplus) && __cplusplus >= 201103L)
 
 #undef  LLONG_MIN
 #undef  LLONG_MAX
 #undef  ULLONG_MAX
 
 #define LLONG_MAX  __LONG_LONG_MAX__
 #define LLONG_MIN  (-__LONG_LONG_MAX__-1LL)
 #define ULLONG_MAX (__LONG_LONG_MAX__*2ULL+1ULL)

clang/lib/Headers/stdarg.h

 #define va_end(ap)          __builtin_va_end(ap)
 #define va_arg(ap, type)    __builtin_va_arg(ap, type)
 
 /* GCC always defines __va_copy, but does not define va_copy unless in c99 mode
  * or -ansi is not specified, since it was not part of C90.
  */
 #define __va_copy(d,s) __builtin_va_copy(d,s)
 
-#if __STDC_VERSION__ >= 199901L || __cplusplus >= 201103L || !defined(__STRICT_ANSI__)
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) ||              \
+    (defined(__cplusplus) && __cplusplus >= 201103L) ||                        \
+    !defined(__STRICT_ANSI__)
 #define va_copy(dest, src)  __builtin_va_copy(dest, src)
 #endif
 
 #ifndef __GNUC_VA_LIST
 #define __GNUC_VA_LIST 1
 typedef __builtin_va_list __gnuc_va_list;
 #endif
 
 #endif /* __STDARG_H */

clang/lib/Headers/stdatomic.h

 #define ATOMIC_INT_LOCK_FREE        __CLANG_ATOMIC_INT_LOCK_FREE
 #define ATOMIC_LONG_LOCK_FREE       __CLANG_ATOMIC_LONG_LOCK_FREE
 #define ATOMIC_LLONG_LOCK_FREE      __CLANG_ATOMIC_LLONG_LOCK_FREE
 #define ATOMIC_POINTER_LOCK_FREE    __CLANG_ATOMIC_POINTER_LOCK_FREE
 
 /* 7.17.2 Initialization */
 
 #define ATOMIC_VAR_INIT(value) (value)
-#if (__STDC_VERSION__ >= 201710L || __cplusplus >= 202002L) &&                 \
+#if ((defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201710L) ||             \
+     (defined(__cplusplus) && __cplusplus >= 202002L)) &&                      \
     !defined(_CLANG_DISABLE_CRT_DEPRECATION_WARNINGS)
 /* ATOMIC_VAR_INIT was deprecated in C17 and C++20. */
 #pragma clang deprecated(ATOMIC_VAR_INIT)
 #endif
 #define atomic_init __c11_atomic_init
 
 /* 7.17.3 Order and consistency */
 

clang/lib/Headers/stdbool.h

 /*===---- stdbool.h - Standard header for booleans -------------------------===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.
  * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  *
  *===-----------------------------------------------------------------------===
  */
 
 #ifndef __STDBOOL_H
 #define __STDBOOL_H
 
 #define __bool_true_false_are_defined 1
 
-#if __STDC_VERSION__ > 201710L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ > 201710L
 /* FIXME: We should be issuing a deprecation warning here, but cannot yet due
  * to system headers which include this header file unconditionally.
  */
 #elif !defined(__cplusplus)
 #define bool _Bool
 #define true 1
 #define false 0
 #elif defined(__GNUC__) && !defined(__STRICT_ANSI__)
 /* Define _Bool as a GNU extension. */
 #define _Bool bool
-#if __cplusplus < 201103L
+#if defined(__cplusplus) && __cplusplus < 201103L
 /* For C++98, define bool, false, true as a GNU extension. */
 #define bool bool
 #define false false
 #define true true
 #endif
 #endif
 
 #endif /* __STDBOOL_H */

clang/lib/Headers/stddef.h

 namespace std { typedef decltype(nullptr) nullptr_t; }
 using ::std::nullptr_t;
 #endif
 #endif
 #undef __need_NULL
 #endif /* defined(__need_NULL) */
 
 #if defined(__need_STDDEF_H_misc)
-#if __STDC_VERSION__ >= 201112L || __cplusplus >= 201103L
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) ||              \
+    (defined(__cplusplus) && __cplusplus >= 201103L)
 #include "__stddef_max_align_t.h"
 #endif
 #define offsetof(t, d) __builtin_offsetof(t, d)
 #undef __need_STDDEF_H_misc
 #endif  /* defined(__need_STDDEF_H_misc) */
 
 /* Some C libraries expect to see a wint_t here. Others (notably MinGW) will use
 __WINT_TYPE__ directly; accommodate both by requiring __need_wint_t */

clang/lib/Headers/stdint.h

  * suboptimal.
  *
  * In violation of the standard, some targets do not implement a type that is
  * wide enough to represent all of the required widths (8-, 16-, 32-, 64-bit).
  * To accommodate these targets, a required minimum-width type is only
  * defined if there exists an exact-width type of equal or greater width.
  */
 
 #ifdef __INT64_TYPE__
 # ifndef __int8_t_defined /* glibc sys/types.h also defines int64_t*/
 typedef __INT64_TYPE__ int64_t;
 # endif /* __int8_t_defined */
 typedef __UINT64_TYPE__ uint64_t;
+# undef __int_least64_t
 # define __int_least64_t int64_t
+# undef __uint_least64_t
 # define __uint_least64_t uint64_t
+# undef __int_least32_t
 # define __int_least32_t int64_t
+# undef __uint_least32_t
 # define __uint_least32_t uint64_t
+# undef __int_least16_t
 # define __int_least16_t int64_t
+# undef __uint_least16_t
 # define __uint_least16_t uint64_t
+# undef __int_least8_t
 # define __int_least8_t int64_t
+# undef __uint_least8_t
 # define __uint_least8_t uint64_t
 #endif /* __INT64_TYPE__ */
 
 #ifdef __int_least64_t
 typedef __int_least64_t int_least64_t;
 typedef __uint_least64_t uint_least64_t;
 typedef __int_least64_t int_fast64_t;
 typedef __uint_least64_t uint_fast64_t;
 #endif /* __int_least64_t */
 
 #ifdef __INT56_TYPE__
 typedef __INT56_TYPE__ int56_t;
 typedef __UINT56_TYPE__ uint56_t;
 typedef int56_t int_least56_t;
 typedef uint56_t uint_least56_t;
 typedef int56_t int_fast56_t;
 typedef uint56_t uint_fast56_t;
+# undef __int_least32_t
 # define __int_least32_t int56_t
+# undef __uint_least32_t
 # define __uint_least32_t uint56_t
+# undef __int_least16_t
 # define __int_least16_t int56_t
+# undef __uint_least16_t
 # define __uint_least16_t uint56_t
+# undef __int_least8_t
 # define __int_least8_t int56_t
+# undef __uint_least8_t
 # define __uint_least8_t uint56_t
 #endif /* __INT56_TYPE__ */
 
 
 #ifdef __INT48_TYPE__
 typedef __INT48_TYPE__ int48_t;
 typedef __UINT48_TYPE__ uint48_t;
 typedef int48_t int_least48_t;
 typedef uint48_t uint_least48_t;
 typedef int48_t int_fast48_t;
 typedef uint48_t uint_fast48_t;
+# undef __int_least32_t
 # define __int_least32_t int48_t
+# undef __uint_least32_t
 # define __uint_least32_t uint48_t
+# undef __int_least16_t
 # define __int_least16_t int48_t
+# undef __uint_least16_t
 # define __uint_least16_t uint48_t
+# undef __int_least8_t
 # define __int_least8_t int48_t
+# undef __uint_least8_t
 # define __uint_least8_t uint48_t
 #endif /* __INT48_TYPE__ */
 
 
 #ifdef __INT40_TYPE__
 typedef __INT40_TYPE__ int40_t;
 typedef __UINT40_TYPE__ uint40_t;
 typedef int40_t int_least40_t;
 typedef uint40_t uint_least40_t;
 typedef int40_t int_fast40_t;
 typedef uint40_t uint_fast40_t;
+# undef __int_least32_t
 # define __int_least32_t int40_t
+# undef __uint_least32_t
 # define __uint_least32_t uint40_t
+# undef __int_least16_t
 # define __int_least16_t int40_t
+# undef __uint_least16_t
 # define __uint_least16_t uint40_t
+# undef __int_least8_t
 # define __int_least8_t int40_t
+# undef __uint_least8_t
 # define __uint_least8_t uint40_t
 #endif /* __INT40_TYPE__ */
 
 
 #ifdef __INT32_TYPE__
 
 # ifndef __int8_t_defined /* glibc sys/types.h also defines int32_t*/
 typedef __INT32_TYPE__ int32_t;
 # endif /* __int8_t_defined */
 
 # ifndef __uint32_t_defined  /* more glibc compatibility */
 # define __uint32_t_defined
 typedef __UINT32_TYPE__ uint32_t;
 # endif /* __uint32_t_defined */
 
+# undef __int_least32_t
 # define __int_least32_t int32_t
+# undef __uint_least32_t
 # define __uint_least32_t uint32_t
+# undef __int_least16_t
 # define __int_least16_t int32_t
+# undef __uint_least16_t
 # define __uint_least16_t uint32_t
+# undef __int_least8_t
 # define __int_least8_t int32_t
+# undef __uint_least8_t
 # define __uint_least8_t uint32_t
 #endif /* __INT32_TYPE__ */
 
 #ifdef __int_least32_t
 typedef __int_least32_t int_least32_t;
 typedef __uint_least32_t uint_least32_t;
 typedef __int_least32_t int_fast32_t;
 typedef __uint_least32_t uint_fast32_t;
 #endif /* __int_least32_t */
 
 #ifdef __INT24_TYPE__
 typedef __INT24_TYPE__ int24_t;
 typedef __UINT24_TYPE__ uint24_t;
 typedef int24_t int_least24_t;
 typedef uint24_t uint_least24_t;
 typedef int24_t int_fast24_t;
 typedef uint24_t uint_fast24_t;
+# undef __int_least16_t
 # define __int_least16_t int24_t
+# undef __uint_least16_t
 # define __uint_least16_t uint24_t
+# undef __int_least8_t
 # define __int_least8_t int24_t
+# undef __uint_least8_t
 # define __uint_least8_t uint24_t
 #endif /* __INT24_TYPE__ */
 
 #ifdef __INT16_TYPE__
 #ifndef __int8_t_defined /* glibc sys/types.h also defines int16_t*/
 typedef __INT16_TYPE__ int16_t;
 #endif /* __int8_t_defined */
 typedef __UINT16_TYPE__ uint16_t;
+# undef __int_least16_t
 # define __int_least16_t int16_t
+# undef __uint_least16_t
 # define __uint_least16_t uint16_t
+# undef __int_least8_t
 # define __int_least8_t int16_t
+# undef __uint_least8_t
 # define __uint_least8_t uint16_t
 #endif /* __INT16_TYPE__ */
 
 #ifdef __int_least16_t
 typedef __int_least16_t int_least16_t;
 typedef __uint_least16_t uint_least16_t;
 typedef __int_least16_t int_fast16_t;
 typedef __uint_least16_t uint_fast16_t;
 #endif /* __int_least16_t */
 
 
 #ifdef __INT8_TYPE__
 #ifndef __int8_t_defined  /* glibc sys/types.h also defines int8_t*/
 typedef __INT8_TYPE__ int8_t;
 #endif /* __int8_t_defined */
 typedef __UINT8_TYPE__ uint8_t;
+# undef __int_least8_t
 # define __int_least8_t int8_t
+# undef __uint_least8_t
 # define __uint_least8_t uint8_t
 #endif /* __INT8_TYPE__ */
 
 #ifdef __int_least8_t
 typedef __int_least8_t int_least8_t;
 typedef __uint_least8_t uint_least8_t;
 typedef __int_least8_t int_fast8_t;
 typedef __uint_least8_t uint_fast8_t;

  */
 
 #define __int_c_join(a, b) a ## b
 #define __int_c(v, suffix) __int_c_join(v, suffix)
 #define __uint_c(v, suffix) __int_c_join(v##U, suffix)
 
 
 #ifdef __INT64_TYPE__
+# undef __int64_c_suffix
+# undef __int32_c_suffix
+# undef __int16_c_suffix
+# undef  __int8_c_suffix
 # ifdef __INT64_C_SUFFIX__
 #  define __int64_c_suffix __INT64_C_SUFFIX__
 #  define __int32_c_suffix __INT64_C_SUFFIX__
 #  define __int16_c_suffix __INT64_C_SUFFIX__
 #  define  __int8_c_suffix __INT64_C_SUFFIX__
-# else
-#  undef __int64_c_suffix
-#  undef __int32_c_suffix
-#  undef __int16_c_suffix
-#  undef  __int8_c_suffix
 # endif /* __INT64_C_SUFFIX__ */
 #endif /* __INT64_TYPE__ */
 
 #ifdef __int_least64_t
 # ifdef __int64_c_suffix
 #  define INT64_C(v) __int_c(v, __int64_c_suffix)
 #  define UINT64_C(v) __uint_c(v, __int64_c_suffix)
 # else
 #  define INT64_C(v) v
 #  define UINT64_C(v) v ## U
 # endif /* __int64_c_suffix */
 #endif /* __int_least64_t */
 
 
 #ifdef __INT56_TYPE__
+# undef __int32_c_suffix
+# undef __int16_c_suffix
+# undef  __int8_c_suffix
 # ifdef __INT56_C_SUFFIX__
 #  define INT56_C(v) __int_c(v, __INT56_C_SUFFIX__)
 #  define UINT56_C(v) __uint_c(v, __INT56_C_SUFFIX__)
 #  define __int32_c_suffix __INT56_C_SUFFIX__
 #  define __int16_c_suffix __INT56_C_SUFFIX__
 #  define __int8_c_suffix  __INT56_C_SUFFIX__
 # else
 #  define INT56_C(v) v
 #  define UINT56_C(v) v ## U
-#  undef __int32_c_suffix
-#  undef __int16_c_suffix
-#  undef  __int8_c_suffix
 # endif /* __INT56_C_SUFFIX__ */
 #endif /* __INT56_TYPE__ */
 
 
 #ifdef __INT48_TYPE__
+# undef __int32_c_suffix
+# undef __int16_c_suffix
+# undef  __int8_c_suffix
 # ifdef __INT48_C_SUFFIX__
 #  define INT48_C(v) __int_c(v, __INT48_C_SUFFIX__)
 #  define UINT48_C(v) __uint_c(v, __INT48_C_SUFFIX__)
 #  define __int32_c_suffix __INT48_C_SUFFIX__
 #  define __int16_c_suffix __INT48_C_SUFFIX__
 #  define __int8_c_suffix  __INT48_C_SUFFIX__
 # else
 #  define INT48_C(v) v
 #  define UINT48_C(v) v ## U
-#  undef __int32_c_suffix
-#  undef __int16_c_suffix
-#  undef  __int8_c_suffix
 # endif /* __INT48_C_SUFFIX__ */
 #endif /* __INT48_TYPE__ */
 
 
 #ifdef __INT40_TYPE__
+# undef __int32_c_suffix
+# undef __int16_c_suffix
+# undef  __int8_c_suffix
 # ifdef __INT40_C_SUFFIX__
 #  define INT40_C(v) __int_c(v, __INT40_C_SUFFIX__)
 #  define UINT40_C(v) __uint_c(v, __INT40_C_SUFFIX__)
 #  define __int32_c_suffix __INT40_C_SUFFIX__
 #  define __int16_c_suffix __INT40_C_SUFFIX__
 #  define __int8_c_suffix  __INT40_C_SUFFIX__
 # else
 #  define INT40_C(v) v
 #  define UINT40_C(v) v ## U
-#  undef __int32_c_suffix
-#  undef __int16_c_suffix
-#  undef  __int8_c_suffix
 # endif /* __INT40_C_SUFFIX__ */
 #endif /* __INT40_TYPE__ */
 
 
 #ifdef __INT32_TYPE__
+# undef __int32_c_suffix
+# undef __int16_c_suffix
+# undef  __int8_c_suffix
 # ifdef __INT32_C_SUFFIX__
 #  define __int32_c_suffix __INT32_C_SUFFIX__
 #  define __int16_c_suffix __INT32_C_SUFFIX__
 #  define __int8_c_suffix  __INT32_C_SUFFIX__
-#else
-#  undef __int32_c_suffix
-#  undef __int16_c_suffix
-#  undef  __int8_c_suffix
 # endif /* __INT32_C_SUFFIX__ */
 #endif /* __INT32_TYPE__ */
 
 #ifdef __int_least32_t
 # ifdef __int32_c_suffix
 #  define INT32_C(v) __int_c(v, __int32_c_suffix)
 #  define UINT32_C(v) __uint_c(v, __int32_c_suffix)
 # else
 #  define INT32_C(v) v
 #  define UINT32_C(v) v ## U
 # endif /* __int32_c_suffix */
 #endif /* __int_least32_t */
 
 
 #ifdef __INT24_TYPE__
+# undef __int16_c_suffix
+# undef  __int8_c_suffix
 # ifdef __INT24_C_SUFFIX__
 #  define INT24_C(v) __int_c(v, __INT24_C_SUFFIX__)
 #  define UINT24_C(v) __uint_c(v, __INT24_C_SUFFIX__)
 #  define __int16_c_suffix __INT24_C_SUFFIX__
 #  define __int8_c_suffix  __INT24_C_SUFFIX__
 # else
 #  define INT24_C(v) v
 #  define UINT24_C(v) v ## U
-#  undef __int16_c_suffix
-#  undef  __int8_c_suffix
 # endif /* __INT24_C_SUFFIX__ */
 #endif /* __INT24_TYPE__ */
 
 
 #ifdef __INT16_TYPE__
+# undef __int16_c_suffix
+# undef  __int8_c_suffix
 # ifdef __INT16_C_SUFFIX__
 #  define __int16_c_suffix __INT16_C_SUFFIX__
 #  define __int8_c_suffix  __INT16_C_SUFFIX__
-#else
-#  undef __int16_c_suffix
-#  undef  __int8_c_suffix
 # endif /* __INT16_C_SUFFIX__ */
 #endif /* __INT16_TYPE__ */
 
 #ifdef __int_least16_t
 # ifdef __int16_c_suffix
 #  define INT16_C(v) __int_c(v, __int16_c_suffix)
 #  define UINT16_C(v) __uint_c(v, __int16_c_suffix)
 # else

  */
 
 #ifdef __INT64_TYPE__
 # define INT64_MAX           INT64_C( 9223372036854775807)
 # define INT64_MIN         (-INT64_C( 9223372036854775807)-1)
 # define UINT64_MAX         UINT64_C(18446744073709551615)
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 # define UINT64_WIDTH         64
 # define INT64_WIDTH          UINT64_WIDTH
 
 # define __UINT_LEAST64_WIDTH UINT64_WIDTH
+# undef __UINT_LEAST32_WIDTH
 # define __UINT_LEAST32_WIDTH UINT64_WIDTH
+# undef __UINT_LEAST16_WIDTH
 # define __UINT_LEAST16_WIDTH UINT64_WIDTH
+# undef __UINT_LEAST8_MAX
 # define __UINT_LEAST8_MAX UINT64_MAX
 #endif /* __STDC_VERSION__ */
 
 # define __INT_LEAST64_MIN   INT64_MIN
 # define __INT_LEAST64_MAX   INT64_MAX
 # define __UINT_LEAST64_MAX UINT64_MAX
+# undef __INT_LEAST32_MIN
 # define __INT_LEAST32_MIN   INT64_MIN
+# undef __INT_LEAST32_MAX
 # define __INT_LEAST32_MAX   INT64_MAX
+# undef __UINT_LEAST32_MAX
 # define __UINT_LEAST32_MAX UINT64_MAX
+# undef __INT_LEAST16_MIN
 # define __INT_LEAST16_MIN   INT64_MIN
+# undef __INT_LEAST16_MAX
 # define __INT_LEAST16_MAX   INT64_MAX
+# undef __UINT_LEAST16_MAX
 # define __UINT_LEAST16_MAX UINT64_MAX
+# undef __INT_LEAST8_MIN
 # define __INT_LEAST8_MIN    INT64_MIN
+# undef __INT_LEAST8_MAX
 # define __INT_LEAST8_MAX    INT64_MAX
+# undef __UINT_LEAST8_MAX
 # define __UINT_LEAST8_MAX  UINT64_MAX
 #endif /* __INT64_TYPE__ */
 
 #ifdef __INT_LEAST64_MIN
 # define INT_LEAST64_MIN   __INT_LEAST64_MIN
 # define INT_LEAST64_MAX   __INT_LEAST64_MAX
 # define UINT_LEAST64_MAX __UINT_LEAST64_MAX
 # define INT_FAST64_MIN    __INT_LEAST64_MIN
 # define INT_FAST64_MAX    __INT_LEAST64_MAX
 # define UINT_FAST64_MAX  __UINT_LEAST64_MAX
 
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) &&  __STDC_VERSION__ >= 202000L
 # define UINT_LEAST64_WIDTH __UINT_LEAST64_WIDTH
 # define INT_LEAST64_WIDTH  UINT_LEAST64_WIDTH
 # define UINT_FAST64_WIDTH  __UINT_LEAST64_WIDTH
 # define INT_FAST64_WIDTH   UINT_FAST64_WIDTH
 #endif /* __STDC_VERSION__ */
 #endif /* __INT_LEAST64_MIN */
 
 
 #ifdef __INT56_TYPE__
 # define INT56_MAX           INT56_C(36028797018963967)
 # define INT56_MIN         (-INT56_C(36028797018963967)-1)
 # define UINT56_MAX         UINT56_C(72057594037927935)
 # define INT_LEAST56_MIN     INT56_MIN
 # define INT_LEAST56_MAX     INT56_MAX
 # define UINT_LEAST56_MAX   UINT56_MAX
 # define INT_FAST56_MIN      INT56_MIN
 # define INT_FAST56_MAX      INT56_MAX
 # define UINT_FAST56_MAX    UINT56_MAX
 
+# undef __INT_LEAST32_MIN
 # define __INT_LEAST32_MIN   INT56_MIN
+# undef __INT_LEAST32_MAX
 # define __INT_LEAST32_MAX   INT56_MAX
+# undef __UINT_LEAST32_MAX
 # define __UINT_LEAST32_MAX UINT56_MAX
+# undef __INT_LEAST16_MIN
 # define __INT_LEAST16_MIN   INT56_MIN
+# undef __INT_LEAST16_MAX
 # define __INT_LEAST16_MAX   INT56_MAX
+# undef __UINT_LEAST16_MAX
 # define __UINT_LEAST16_MAX UINT56_MAX
+# undef __INT_LEAST8_MIN
 # define __INT_LEAST8_MIN    INT56_MIN
+# undef __INT_LEAST8_MAX
 # define __INT_LEAST8_MAX    INT56_MAX
+# undef __UINT_LEAST8_MAX
 # define __UINT_LEAST8_MAX  UINT56_MAX
 
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 # define UINT56_WIDTH         56
 # define INT56_WIDTH          UINT56_WIDTH
 # define UINT_LEAST56_WIDTH   UINT56_WIDTH
 # define INT_LEAST56_WIDTH    UINT_LEAST56_WIDTH
 # define UINT_FAST56_WIDTH    UINT56_WIDTH
 # define INT_FAST56_WIDTH     UINT_FAST56_WIDTH
+# undef __UINT_LEAST32_WIDTH
 # define __UINT_LEAST32_WIDTH UINT56_WIDTH
+# undef __UINT_LEAST16_WIDTH
 # define __UINT_LEAST16_WIDTH UINT56_WIDTH
+# undef __UINT_LEAST8_WIDTH
 # define __UINT_LEAST8_WIDTH  UINT56_WIDTH
 #endif /* __STDC_VERSION__ */
 #endif /* __INT56_TYPE__ */
 
 
 #ifdef __INT48_TYPE__
 # define INT48_MAX           INT48_C(140737488355327)
 # define INT48_MIN         (-INT48_C(140737488355327)-1)
 # define UINT48_MAX         UINT48_C(281474976710655)
 # define INT_LEAST48_MIN     INT48_MIN
 # define INT_LEAST48_MAX     INT48_MAX
 # define UINT_LEAST48_MAX   UINT48_MAX
 # define INT_FAST48_MIN      INT48_MIN
 # define INT_FAST48_MAX      INT48_MAX
 # define UINT_FAST48_MAX    UINT48_MAX
 
+# undef __INT_LEAST32_MIN
 # define __INT_LEAST32_MIN   INT48_MIN
+# undef __INT_LEAST32_MAX
 # define __INT_LEAST32_MAX   INT48_MAX
+# undef __UINT_LEAST32_MAX
 # define __UINT_LEAST32_MAX UINT48_MAX
+# undef __INT_LEAST16_MIN
 # define __INT_LEAST16_MIN   INT48_MIN
+# undef __INT_LEAST16_MAX
 # define __INT_LEAST16_MAX   INT48_MAX
+# undef __UINT_LEAST16_MAX
 # define __UINT_LEAST16_MAX UINT48_MAX
+# undef __INT_LEAST8_MIN
 # define __INT_LEAST8_MIN    INT48_MIN
+# undef __INT_LEAST8_MAX
 # define __INT_LEAST8_MAX    INT48_MAX
+# undef __UINT_LEAST8_MAX
 # define __UINT_LEAST8_MAX  UINT48_MAX
 
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 #define UINT48_WIDTH         48
 #define INT48_WIDTH          UINT48_WIDTH
 #define UINT_LEAST48_WIDTH   UINT48_WIDTH
 #define INT_LEAST48_WIDTH    UINT_LEAST48_WIDTH
 #define UINT_FAST48_WIDTH    UINT48_WIDTH
 #define INT_FAST48_WIDTH     UINT_FAST48_WIDTH
+#undef __UINT_LEAST32_WIDTH
 #define __UINT_LEAST32_WIDTH UINT48_WIDTH
+# undef __UINT_LEAST16_WIDTH
 #define __UINT_LEAST16_WIDTH UINT48_WIDTH
+# undef __UINT_LEAST8_WIDTH
 #define __UINT_LEAST8_WIDTH  UINT48_WIDTH
 #endif /* __STDC_VERSION__ */
 #endif /* __INT48_TYPE__ */
 
 
 #ifdef __INT40_TYPE__
 # define INT40_MAX           INT40_C(549755813887)
 # define INT40_MIN         (-INT40_C(549755813887)-1)
 # define UINT40_MAX         UINT40_C(1099511627775)
 # define INT_LEAST40_MIN     INT40_MIN
 # define INT_LEAST40_MAX     INT40_MAX
 # define UINT_LEAST40_MAX   UINT40_MAX
 # define INT_FAST40_MIN      INT40_MIN
 # define INT_FAST40_MAX      INT40_MAX
 # define UINT_FAST40_MAX    UINT40_MAX
 
+# undef __INT_LEAST32_MIN
 # define __INT_LEAST32_MIN   INT40_MIN
+# undef __INT_LEAST32_MAX
 # define __INT_LEAST32_MAX   INT40_MAX
+# undef __UINT_LEAST32_MAX
 # define __UINT_LEAST32_MAX UINT40_MAX
+# undef __INT_LEAST16_MIN
 # define __INT_LEAST16_MIN   INT40_MIN
+# undef __INT_LEAST16_MAX
 # define __INT_LEAST16_MAX   INT40_MAX
+# undef __UINT_LEAST16_MAX
 # define __UINT_LEAST16_MAX UINT40_MAX
+# undef __INT_LEAST8_MIN
 # define __INT_LEAST8_MIN    INT40_MIN
+# undef __INT_LEAST8_MAX
 # define __INT_LEAST8_MAX    INT40_MAX
+# undef __UINT_LEAST8_MAX
 # define __UINT_LEAST8_MAX  UINT40_MAX
 
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 # define UINT40_WIDTH         40
 # define INT40_WIDTH          UINT40_WIDTH
 # define UINT_LEAST40_WIDTH   UINT40_WIDTH
 # define INT_LEAST40_WIDTH    UINT_LEAST40_WIDTH
 # define UINT_FAST40_WIDTH    UINT40_WIDTH
 # define INT_FAST40_WIDTH     UINT_FAST40_WIDTH
+# undef __UINT_LEAST32_WIDTH
 # define __UINT_LEAST32_WIDTH UINT40_WIDTH
+# undef __UINT_LEAST16_WIDTH
 # define __UINT_LEAST16_WIDTH UINT40_WIDTH
+# undef __UINT_LEAST8_WIDTH
 # define __UINT_LEAST8_WIDTH  UINT40_WIDTH
 #endif /* __STDC_VERSION__ */
 #endif /* __INT40_TYPE__ */
 
 
 #ifdef __INT32_TYPE__
 # define INT32_MAX           INT32_C(2147483647)
 # define INT32_MIN         (-INT32_C(2147483647)-1)
 # define UINT32_MAX         UINT32_C(4294967295)
 
+# undef __INT_LEAST32_MIN
 # define __INT_LEAST32_MIN   INT32_MIN
+# undef __INT_LEAST32_MAX
 # define __INT_LEAST32_MAX   INT32_MAX
+# undef __UINT_LEAST32_MAX
 # define __UINT_LEAST32_MAX UINT32_MAX
+# undef __INT_LEAST16_MIN
 # define __INT_LEAST16_MIN   INT32_MIN
+# undef __INT_LEAST16_MAX
 # define __INT_LEAST16_MAX   INT32_MAX
+# undef __UINT_LEAST16_MAX
 # define __UINT_LEAST16_MAX UINT32_MAX
+# undef __INT_LEAST8_MIN
 # define __INT_LEAST8_MIN    INT32_MIN
+# undef __INT_LEAST8_MAX
 # define __INT_LEAST8_MAX    INT32_MAX
+# undef __UINT_LEAST8_MAX
 # define __UINT_LEAST8_MAX  UINT32_MAX
 
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 # define UINT32_WIDTH         32
 # define INT32_WIDTH          UINT32_WIDTH
+# undef __UINT_LEAST32_WIDTH
 # define __UINT_LEAST32_WIDTH UINT32_WIDTH
+# undef __UINT_LEAST16_WIDTH
 # define __UINT_LEAST16_WIDTH UINT32_WIDTH
+# undef __UINT_LEAST8_WIDTH
 # define __UINT_LEAST8_WIDTH  UINT32_WIDTH
 #endif /* __STDC_VERSION__ */
 #endif /* __INT32_TYPE__ */
 
 #ifdef __INT_LEAST32_MIN
 # define INT_LEAST32_MIN   __INT_LEAST32_MIN
 # define INT_LEAST32_MAX   __INT_LEAST32_MAX
 # define UINT_LEAST32_MAX __UINT_LEAST32_MAX
 # define INT_FAST32_MIN    __INT_LEAST32_MIN
 # define INT_FAST32_MAX    __INT_LEAST32_MAX
 # define UINT_FAST32_MAX  __UINT_LEAST32_MAX
 
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 # define UINT_LEAST32_WIDTH __UINT_LEAST32_WIDTH
 # define INT_LEAST32_WIDTH  UINT_LEAST32_WIDTH
 # define UINT_FAST32_WIDTH  __UINT_LEAST32_WIDTH
 # define INT_FAST32_WIDTH   UINT_FAST32_WIDTH
 #endif /* __STDC_VERSION__ */
 #endif /* __INT_LEAST32_MIN */
 
 
 #ifdef __INT24_TYPE__
 # define INT24_MAX           INT24_C(8388607)
 # define INT24_MIN         (-INT24_C(8388607)-1)
 # define UINT24_MAX         UINT24_C(16777215)
 # define INT_LEAST24_MIN     INT24_MIN
 # define INT_LEAST24_MAX     INT24_MAX
 # define UINT_LEAST24_MAX   UINT24_MAX
 # define INT_FAST24_MIN      INT24_MIN
 # define INT_FAST24_MAX      INT24_MAX
 # define UINT_FAST24_MAX    UINT24_MAX
 
+# undef __INT_LEAST16_MIN
 # define __INT_LEAST16_MIN   INT24_MIN
+# undef __INT_LEAST16_MAX
 # define __INT_LEAST16_MAX   INT24_MAX
+# undef __UINT_LEAST16_MAX
 # define __UINT_LEAST16_MAX UINT24_MAX
+# undef __INT_LEAST8_MIN
 # define __INT_LEAST8_MIN    INT24_MIN
+# undef __INT_LEAST8_MAX
 # define __INT_LEAST8_MAX    INT24_MAX
+# undef __UINT_LEAST8_MAX
 # define __UINT_LEAST8_MAX  UINT24_MAX
 
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 # define UINT24_WIDTH         24
 # define INT24_WIDTH          UINT24_WIDTH
 # define UINT_LEAST24_WIDTH   UINT24_WIDTH
 # define INT_LEAST24_WIDTH    UINT_LEAST24_WIDTH
 # define UINT_FAST24_WIDTH    UINT24_WIDTH
 # define INT_FAST24_WIDTH     UINT_FAST24_WIDTH
+# undef __UINT_LEAST16_WIDTH
 # define __UINT_LEAST16_WIDTH UINT24_WIDTH
+# undef __UINT_LEAST8_WIDTH
 # define __UINT_LEAST8_WIDTH  UINT24_WIDTH
 #endif /* __STDC_VERSION__ */
 #endif /* __INT24_TYPE__ */
 
 
 #ifdef __INT16_TYPE__
 #define INT16_MAX            INT16_C(32767)
 #define INT16_MIN          (-INT16_C(32767)-1)
 #define UINT16_MAX          UINT16_C(65535)
 
+# undef __INT_LEAST16_MIN
 # define __INT_LEAST16_MIN   INT16_MIN
+# undef __INT_LEAST16_MAX
 # define __INT_LEAST16_MAX   INT16_MAX
+# undef __UINT_LEAST16_MAX
 # define __UINT_LEAST16_MAX UINT16_MAX
+# undef __INT_LEAST8_MIN
 # define __INT_LEAST8_MIN    INT16_MIN
+# undef __INT_LEAST8_MAX
 # define __INT_LEAST8_MAX    INT16_MAX
+# undef __UINT_LEAST8_MAX
 # define __UINT_LEAST8_MAX  UINT16_MAX
 
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 # define UINT16_WIDTH         16
 # define INT16_WIDTH          UINT16_WIDTH
+# undef __UINT_LEAST16_WIDTH
 # define __UINT_LEAST16_WIDTH UINT16_WIDTH
+# undef __UINT_LEAST8_WIDTH
 # define __UINT_LEAST8_WIDTH  UINT16_WIDTH
 #endif /* __STDC_VERSION__ */
 #endif /* __INT16_TYPE__ */
 
 #ifdef __INT_LEAST16_MIN
 # define INT_LEAST16_MIN   __INT_LEAST16_MIN
 # define INT_LEAST16_MAX   __INT_LEAST16_MAX
 # define UINT_LEAST16_MAX __UINT_LEAST16_MAX
 # define INT_FAST16_MIN    __INT_LEAST16_MIN
 # define INT_FAST16_MAX    __INT_LEAST16_MAX
 # define UINT_FAST16_MAX  __UINT_LEAST16_MAX
 
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 # define UINT_LEAST16_WIDTH __UINT_LEAST16_WIDTH
 # define INT_LEAST16_WIDTH  UINT_LEAST16_WIDTH
 # define UINT_FAST16_WIDTH  __UINT_LEAST16_WIDTH
 # define INT_FAST16_WIDTH   UINT_FAST16_WIDTH
 #endif /* __STDC_VERSION__ */
 #endif /* __INT_LEAST16_MIN */
 
 
 #ifdef __INT8_TYPE__
 # define INT8_MAX            INT8_C(127)
 # define INT8_MIN          (-INT8_C(127)-1)
 # define UINT8_MAX          UINT8_C(255)
 
+# undef __INT_LEAST8_MIN
 # define __INT_LEAST8_MIN    INT8_MIN
+# undef __INT_LEAST8_MAX
 # define __INT_LEAST8_MAX    INT8_MAX
+# undef __UINT_LEAST8_MAX
 # define __UINT_LEAST8_MAX  UINT8_MAX
 
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 # define UINT8_WIDTH         8
 # define INT8_WIDTH          UINT8_WIDTH
+# undef __UINT_LEAST8_WIDTH
 # define __UINT_LEAST8_WIDTH UINT8_WIDTH
 #endif /* __STDC_VERSION__ */
 #endif /* __INT8_TYPE__ */
 
 #ifdef __INT_LEAST8_MIN
 # define INT_LEAST8_MIN   __INT_LEAST8_MIN
 # define INT_LEAST8_MAX   __INT_LEAST8_MAX
 # define UINT_LEAST8_MAX __UINT_LEAST8_MAX
 # define INT_FAST8_MIN    __INT_LEAST8_MIN
 # define INT_FAST8_MAX    __INT_LEAST8_MAX
 # define UINT_FAST8_MAX  __UINT_LEAST8_MAX
 
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 # define UINT_LEAST8_WIDTH __UINT_LEAST8_WIDTH
 # define INT_LEAST8_WIDTH  UINT_LEAST8_WIDTH
 # define UINT_FAST8_WIDTH  __UINT_LEAST8_WIDTH
 # define INT_FAST8_WIDTH   UINT_FAST8_WIDTH
 #endif /* __STDC_VERSION__ */
 #endif /* __INT_LEAST8_MIN */
 
 /* Some utility macros */

 #define UINTPTR_MAX   __UINTPTR_MAX__
 #define PTRDIFF_MIN (-__PTRDIFF_MAX__-1)
 #define PTRDIFF_MAX   __PTRDIFF_MAX__
 #define    SIZE_MAX      __SIZE_MAX__
 
 /* C2x 7.20.2.4 Width of integer types capable of holding object pointers. */
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 /* NB: The C standard requires that these be the same value, but the compiler
    exposes separate internal width macros. */
 #define INTPTR_WIDTH  __INTPTR_WIDTH__
 #define UINTPTR_WIDTH __UINTPTR_WIDTH__
 #endif
 
 /* ISO9899:2011 7.20 (C11 Annex K): Define RSIZE_MAX if __STDC_WANT_LIB_EXT1__
  * is enabled. */
 #if defined(__STDC_WANT_LIB_EXT1__) && __STDC_WANT_LIB_EXT1__ >= 1
 #define   RSIZE_MAX            (SIZE_MAX >> 1)
 #endif
 
 /* C99 7.18.2.5 Limits of greatest-width integer types. */
 #define  INTMAX_MIN (-__INTMAX_MAX__-1)
 #define  INTMAX_MAX   __INTMAX_MAX__
 #define UINTMAX_MAX  __UINTMAX_MAX__
 
 /* C2x 7.20.2.5 Width of greatest-width integer types. */
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 /* NB: The C standard requires that these be the same value, but the compiler
    exposes separate internal width macros. */
 #define INTMAX_WIDTH __INTMAX_WIDTH__
 #define UINTMAX_WIDTH __UINTMAX_WIDTH__
 #endif
 
 /* C99 7.18.3 Limits of other integer types. */
 #define SIG_ATOMIC_MIN __INTN_MIN(__SIG_ATOMIC_WIDTH__)

 
 /* 7.18.4.2 Macros for greatest-width integer constants. */
 #define  INTMAX_C(v) __int_c(v,  __INTMAX_C_SUFFIX__)
 #define UINTMAX_C(v) __int_c(v, __UINTMAX_C_SUFFIX__)
 
 /* C2x 7.20.3.x Width of other integer types. */
 /* FIXME: This is using the placeholder dates Clang produces for these macros
    in C2x mode; switch to the correct values once they've been published. */
-#if __STDC_VERSION__ >= 202000L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L
 #define PTRDIFF_WIDTH    __PTRDIFF_WIDTH__
 #define SIG_ATOMIC_WIDTH __SIG_ATOMIC_WIDTH__
 #define SIZE_WIDTH       __SIZE_WIDTH__
 #define WCHAR_WIDTH      __WCHAR_WIDTH__
 #define WINT_WIDTH       __WINT_WIDTH__
 #endif
 
 #endif /* __STDC_HOSTED__ */
 #endif /* __CLANG_STDINT_H */

clang/lib/Headers/stdnoreturn.h

 /*===---- stdnoreturn.h - Standard header for noreturn macro ---------------===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.
  * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  *
  *===-----------------------------------------------------------------------===
  */
 
 #ifndef __STDNORETURN_H
 #define __STDNORETURN_H
 
 #define noreturn _Noreturn
 #define __noreturn_is_defined 1
 
-#if __STDC_VERSION__ > 201710L &&                                              \
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ > 201710L) &&               \
     !defined(_CLANG_DISABLE_CRT_DEPRECATION_WARNINGS)
 /* The noreturn macro is deprecated in C2x. We do not mark it as such because
    including the header file in C2x is also deprecated and we do not want to
    issue a confusing diagnostic for code which includes <stdnoreturn.h>
    followed by code that writes [[noreturn]]. The issue with such code is not
    with the attribute, or the use of 'noreturn', but the inclusion of the
    header. */
 /* FIXME: We should be issuing a deprecation warning here, but cannot yet due
  * to system headers which include this header file unconditionally.
  */
 #endif
 
 #endif /* __STDNORETURN_H */

clang/lib/Headers/velintrin.h

 /*===---- velintrin.h - VEL intrinsics for VE ------------------------------===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.
  * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  *
  *===-----------------------------------------------------------------------===
  */
 #ifndef __VEL_INTRIN_H__
 #define __VEL_INTRIN_H__
 
 // Vector registers
 typedef double __vr __attribute__((__vector_size__(2048)));
 
 // Vector mask registers
-#if __STDC_VERSION__ >= 199901L
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
 // For C99
 typedef _Bool __vm    __attribute__((ext_vector_type(256)));
 typedef _Bool __vm256 __attribute__((ext_vector_type(256)));
 typedef _Bool __vm512 __attribute__((ext_vector_type(512)));
 #else
 #ifdef __cplusplus
 // For C++
 typedef bool __vm    __attribute__((ext_vector_type(256)));