[libc] [llvm] [libc] add remaining epoll functions, pipe (PR #84587)

[Nick Desaulniers via llvm-commits]

https://github.com/nickdesaulniers approved this pull request.

Don't forget to pack the `struct epoll_event` for x86_64 before you land this.

https://github.com/llvm/llvm-project/pull/84587