[libc] Add fenv functions to arm32 baremetal config.

[sivachandra]

Summary

Also, an "arm" subfolder for baremetal config has been added.

libc/config/baremetal/api.td

 include "config/public_api.td"
 
 include "spec/stdc.td"
 
 def CTypeAPI : PublicAPI<"ctype.h"> {
 }
 
+def FEnvAPI : PublicAPI<"fenv.h"> {
+  let Types = ["fenv_t", "fexcept_t"];
+}
+
 def IntTypesAPI : PublicAPI<"inttypes.h"> {
   let Types = ["imaxdiv_t"];
 }
 
 def StdlibAPI : PublicAPI<"stdlib.h"> {
   let Types = [
     "div_t",
     "ldiv_t",

libc/config/baremetal/arm/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
     libc.src.stdlib.strtol
     libc.src.stdlib.strtold
     libc.src.stdlib.strtoll
     libc.src.stdlib.strtoul
     libc.src.stdlib.strtoull
 )
 
 set(TARGET_LIBM_ENTRYPOINTS
+    # fenv.h entrypoints
+    libc.src.fenv.feclearexcept
+    libc.src.fenv.fedisableexcept
+    libc.src.fenv.feenableexcept
+    libc.src.fenv.fegetenv
+    libc.src.fenv.fegetexcept
+    libc.src.fenv.fegetexceptflag
+    libc.src.fenv.fegetround
+    libc.src.fenv.feholdexcept
+    libc.src.fenv.fesetenv
+    libc.src.fenv.fesetexceptflag
+    libc.src.fenv.fesetround
+    libc.src.fenv.feraiseexcept
+    libc.src.fenv.fetestexcept
+    libc.src.fenv.feupdateenv
+
     # math.h entrypoints
     libc.src.math.fabs
     libc.src.math.fabsf
     libc.src.math.fabsl
     libc.src.math.fdim
     libc.src.math.fdimf
     libc.src.math.fdiml
     libc.src.math.fmax

libc/config/baremetal/arm/headers.txt

 set(TARGET_PUBLIC_HEADERS
     libc.include.ctype
+    libc.include.fenv
     libc.include.errno
     libc.include.inttypes
     libc.include.math
     libc.include.stdlib
     libc.include.string
 )

libc/include/llvm-libc-types/fenv_t.h

 //===-- Definition of type fenv_t -----------------------------------------===//
 //
 // 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 __LLVM_LIBC_TYPES_FENV_T_H__
 #define __LLVM_LIBC_TYPES_FENV_T_H__
 
 #ifdef __aarch64__
 typedef struct {
   unsigned char __control_word[4];
   unsigned char __status_word[4];
 } fenv_t;
-#endif
-#ifdef __x86_64__
+#elif defined(__x86_64__)
 typedef struct {
   unsigned char __x86_status[28];
   unsigned char __mxcsr[4];
 } fenv_t;
+#elif defined(__arm__) || defined(_M_ARM)
+typedef struct {
+  unsigned int __fpscr;
+} fenv_t;
+#else
+#error "fenv_t not defined for your platform"
 #endif
 
 #endif // __LLVM_LIBC_TYPES_FENV_T_H__