[libc-commits] [libc] [libc] move non <bit> functions to math_extras (PR #84818)

[Nick Desaulniers via libc-commits]

nickdesaulniers wrote:

(I probably need to rebase this on top of https://github.com/llvm/llvm-project/pull/84670)

https://github.com/llvm/llvm-project/pull/84818