[clang] fix bug that undefined internal is a warning only for -pedantic-errors (PR #98016)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

Okay, the Windows issue seems to have gone away with a full rebuild, which makes *way* more sense to me. :-) So I think it's just the `llvm-clang-x86_64-sie-ubuntu-fast` issue that needs to be resolved.

https://github.com/llvm/llvm-project/pull/98016