[libc-commits] [libc] [libc] clean up futex usage (PR #91163)

[Michael Jones via libc-commits]

michaelrj-google wrote:

I would say that using `CLOCK_MONOTONIC` instead of `CLOCK_REALTIME` is probably a good idea, but should be toggleable with a flag.

https://github.com/llvm/llvm-project/pull/91163