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

[Nick Desaulniers via libc-commits]

https://github.com/nickdesaulniers commented:

I'm very happy with the result here! Two minor style nits, then this LGTM.

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