[clang] [Clang] Diagnose conflict between always_inline/noinline attributes (PR #215173)

[Kenzo Tjandra via cfe-commits]

ketjandr wrote:

Hi @erichkeane and @AaronBallman, I'm tagging you here since this is my first contribution and I can't add reviewers directly. I'd greatly appreciate your review.

https://github.com/llvm/llvm-project/pull/215173