We need to refactor ilogbf to be header-only, constexpr (if possible), shared math function.
We need make sure that the code compiles with the supported compilers and build systems in LLVM libc: Clang, GCC12.2, CMake and Bazel.

Part of #147386

in preparation for: https://discourse.llvm.org/t/rfc-make-clang-builtin-math-functions-constexpr-with-llvm-libc-to-support-c-23-constexpr-math-functions/86450