[libc][NFC] Simplify how the definiton of NULL macro is added to string.h.

[sivachandra]

Summary

We do not list macro definitions in api.td files anymore. Not all macros
definitions have been moved out. This change moves the definition of the
NULL macro out.

[jhuber6]

I'm guessing this is part of the ongoing effort to move away from tablegen?

[sivachandra]

In D140376#4007761, @jhuber6 wrote:

I'm guessing this is part of the ongoing effort to move away from tablegen?

Yes. I will also be adding a "baremetal" config. I don't want to repeat the definition in its api.td file yet again.

libc/config/gpu/api.td

 include "config/public_api.td"
 
 include "spec/stdc.td"
 
-def NullMacro : MacroDef<"NULL"> {
-  let Defn = [{
-    #define __need_NULL
-    #include <stddef.h>
-  }];
-}
-
 def StringAPI : PublicAPI<"string.h"> {
   let Types = ["size_t"];
-
-  let Macros = [
-    NullMacro,
-  ];
 }

libc/config/linux/api.td

def StaticAssertMacro : MacroDef<"static_assert"> {
   let Defn = [{
     #ifndef __cplusplus
     #undef static_assert
     #define static_assert _Static_assert
     #endif
   }];
 }
 
-def NullMacro : MacroDef<"NULL"> {
-  let Defn = [{
-    #define __need_NULL
-    #include <stddef.h>
-  }];
-}
-
 def AssertAPI : PublicAPI<"assert.h"> {
   let Macros = [
     AssertMacro,
     StaticAssertMacro,
   ];
 }
 
 def CTypeAPI : PublicAPI<"ctype.h"> {
let Macros = [
 
     SimpleMacroDef<"FE_DFL_ENV", "((fenv_t *)-1)">,
   ];
   let Types = ["fenv_t", "fexcept_t"];
 }
 
 def StringAPI : PublicAPI<"string.h"> {
   let Types = ["size_t"];
-
-  let Macros = [
-    NullMacro,
-  ];
 }
 
 def StdIOAPI : PublicAPI<"stdio.h"> {
   let Macros = [
     SimpleMacroDef<"stderr", "stderr">,
     SimpleMacroDef<"stdin", "stdin">,
     SimpleMacroDef<"stdout", "stdout">,
     SimpleMacroDef<"_IOFBF", "0">,

libc/include/CMakeLists.txt

 )
 
 add_gen_header(
   string
   DEF_FILE string.h.def
   GEN_HDR string.h
   DEPENDS
     .llvm_libc_common_h
+    .llvm-libc-macros.null_macro
     .llvm-libc-types.size_t
 )
 
 add_gen_header(
   time
   DEF_FILE time.h.def
   GEN_HDR time.h
   DEPENDS

libc/include/llvm-libc-macros/CMakeLists.txt

 add_subdirectory(linux)
 
 add_header(
   generic_error_number_macros
   HDR
     generic-error-number-macros.h
 )
 
 add_header(
+  null_macro
+  HDR
+    null-macro.h
+)
+
+add_header(
   fcntl_macros
   HDR
     fcntl-macros.h
   DEPENDS
     .linux.fcntl_macros
 )
 
 add_header(

libc/include/llvm-libc-macros/null-macro.h

-//===-- C standard library header string.h --------------------------------===//
+//===-- Definition of the NULL 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 LLVM_LIBC_STRING_H
-#define LLVM_LIBC_STRING_H
+#ifndef __LLVM_LIBC_MACROS_NULL_MACRO_H
+#define __LLVM_LIBC_MACROS_NULL_MACRO_H
 
-#include <__llvm-libc-common.h>
+#define __need_NULL
+#include <stddef.h>
 
-%%public_api()
-
-#endif // LLVM_LIBC_STRING_H
+#endif // __LLVM_LIBC_MACROS_NULL_MACRO_H

libc/include/string.h.def

 //===-- C standard library header string.h --------------------------------===//
 //
 // 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_STRING_H
 #define LLVM_LIBC_STRING_H
 
 #include <__llvm-libc-common.h>
 
+#include <llvm-libc-macros/null-macro.h>
+
 %%public_api()
 
 #endif // LLVM_LIBC_STRING_H