[llvm] [libc] [reland][libc] add epoll_wait functions (PR #79635)

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

in https://github.com/llvm/llvm-project/pull/79635/commits/c88c4da95feade9e78f77017458e739d30ed0ea2, did you intend to leave those includes commented out? If so, should we add a TODO describing what needs to be done to remove or replace those comments in the future? You may have an idea, but it's unclear to me.

https://github.com/llvm/llvm-project/pull/79635