[clang] Ensure proper NULL macro definition for system include files. (PR #149176)

[Hubert Tong via cfe-commits]

================
@@ -39,6 +39,25 @@ set(core_files
   varargs.h
   )
 
+set(aix_wrapper_files
+  dbm.h
+  stdio.h
+  stdlib.h
+  string.h
+  time.h
+  unistd.h
+  wchar.h
+  )
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hubert-reinterpretcast wrote:

At least `locale.h` was also affected.

https://github.com/llvm/llvm-project/pull/149176