[cherry-pick swift/release/6.0][clang][headers] Including stddef.h always redefines NULL#9003

fredriss merged 1 commit intoswiftlang:swift/release/6.0swiftlang/llvm-project:swift/release/6.0from

ian-twilightcoder:null_overwriteian-twilightcoder/llvm-project:null_overwriteCopy head branch name to clipboard