[clang] [clang] Warn on umask() argument bits outside 0777 (PR #198130)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

I think this is heading in the right direction; a few drive-by comments while waiting to see how precommit CI likes the changes.

https://github.com/llvm/llvm-project/pull/198130