[libc] [llvm] [libc][NFC] Split 'builtin_wrapper' into 'bit' and 'math_extras' (PR #72998)

[Guillaume Chatelet via llvm-commits]

gchatelet wrote:

Split `builtin_wrapper.h` into `bit.h` and `math_extras.h` to mimic LLVM `llvm/ADT/Bit.h` and `llvm/Support/MathExtras.h`.
Also added unittest place holders.

https://github.com/llvm/llvm-project/pull/72998