[libc] Add NULL macro definitions to header files (#142764)

By the C standard, <locale.h>, <stddef.h> <stdio.h>, <stdlib.h>,
<string.h>, <time.h>, and <wchar.h> require NULL to be defined.

libc/include/CMakeLists.txt

@@ -255,6 +255,7 @@ add_header_macro(
   time.h
   DEPENDS
     .llvm_libc_common_h
+    .llvm-libc-macros.null_macro
     .llvm-libc-macros.time_macros
     .llvm-libc-types.clock_t
     .llvm-libc-types.time_t
@@ -329,6 +330,7 @@ add_header_macro(
   stdio.h
   DEPENDS
     .llvm-libc-macros.file_seek_macros
+    .llvm-libc-macros.null_macro
     .llvm-libc-macros.stdio_macros
     .llvm-libc-types.FILE
     .llvm-libc-types.cookie_io_functions_t
@@ -343,6 +345,7 @@ add_header_macro(
   ../libc/include/stdlib.yaml
   stdlib.h
   DEPENDS
+    .llvm-libc-macros.null_macro
     .llvm-libc-macros.stdlib_macros
     .llvm-libc-types.__atexithandler_t
     .llvm-libc-types.__qsortcompare_t
@@ -709,6 +712,7 @@ add_header_macro(
   wchar.h
   DEPENDS
     .llvm_libc_common_h
+    .llvm-libc-macros.null_macro
     .llvm-libc-macros.wchar_macros
     .llvm-libc-types.mbstate_t
     .llvm-libc-types.size_t
@@ -723,6 +727,7 @@ add_header_macro(
   DEPENDS
     .llvm_libc_common_h
     .llvm-libc-macros.locale_macros
+    .llvm-libc-macros.null_macro
     .llvm-libc-types.locale_t
     .llvm-libc-types.struct_lconv
 )

libc/include/locale.yaml

@@ -1,5 +1,8 @@
 header: locale.h
 header_template: locale.h.def
+macros:
+  - macro_name: NULL
+    macro_header: null-macro.h
 types:
   - type_name: locale_t
   - type_name: struct_lconv

libc/include/stdio.yaml

@@ -1,6 +1,8 @@
 header: stdio.h
 header_template: stdio.h.def
 macros:
+  - macro_name: NULL
+    macro_header: null-macro.h
   - macro_name: stdout
     macro_value: stdout
   - macro_name: stdin

libc/include/stdlib.yaml

@@ -4,7 +4,9 @@ standards:
   - stdc
 merge_yaml_files:
   - stdlib-malloc.yaml
-macros: []
+macros:
+  - macro_name: NULL
+    macro_header: null-macro.h
 types:
   - type_name: __atexithandler_t
   - type_name: __qsortcompare_t

libc/include/string.h.def

@@ -11,8 +11,6 @@
 
 #include "__llvm-libc-common.h"
 
-#include "llvm-libc-macros/null-macro.h"
-
 %%public_api()
 
 #endif // LLVM_LIBC_STRING_H

libc/include/string.yaml

@@ -1,6 +1,8 @@
 header: string.h
 header_template: string.h.def
-macros: []
+macros:
+  - macro_name: NULL
+    macro_header: null-macro.h
 types:
   - type_name: locale_t
   - type_name: size_t

libc/include/time.yaml

@@ -1,6 +1,8 @@
 header: time.h
 header_template: time.h.def
-macros: []
+macros:
+  - macro_name: NULL
+    macro_header: null-macro.h
 types:
   - type_name: struct_timeval
   - type_name: clockid_t

libc/include/wchar.yaml

@@ -1,6 +1,8 @@
 header: wchar.h
 header_template: wchar.h.def
-macros: []
+macros:
+  - macro_name: NULL
+    macro_header: null-macro.h
 types:
   - type_name: size_t
   - type_name: wint_t