[clang] [AIX] Detect `#pragma mc_func` (PR #99888)

[Qiongsi Wu via cfe-commits]

qiongsiwu wrote:

> My preference is for this to be on-by-default (then it shows its utility), and I'd like to see those changes in the 19.x release (which means we'd need to turn this around fairly quickly as we've already put out rc1).

Sounds good! Thanks again for your input @AaronBallman ! 

https://github.com/llvm/llvm-project/pull/101336 is setup to turn on the check by default. 

https://github.com/llvm/llvm-project/pull/99888