[libc-commits] [libc] [libc] Replace `MutexLock` with `cpp::lock_guard` (PR #89340)

[Vlad Mishel via libc-commits]

vmishelcs wrote:

> Just a little nit, otherwise LGTM. Can you land this PR or do you need me to land it?

Addressed your comment :)
I don't have write permissions so if you feel that my code meets LLVM standards I'll need someone to merge this PR.

https://github.com/llvm/llvm-project/pull/89340