[clang] [clang-tools-extra] [llvm] [clang][modules] stdarg.h and stddef.h shouldn't directly declare anything (PR #90676)

[Michael Spencer via cfe-commits]

https://github.com/Bigcheese commented:

I think I like this as a solution, although I wonder if __stdarg_guard_macro.h would be a better name. The name now somewhat implies that it contains the macros that stddef and stdarg define.

https://github.com/llvm/llvm-project/pull/90676