[libc] Consolidate floating point utils into a single utils library.

A new utils library named 'fputil' is added. This library is used in
math tests and the MPFR wrapper. The math implementations will be
modified to use this library in a later round.

Reviewers: phosek

Differential Revision: https://reviews.llvm.org/D79724

GitOrigin-RevId: 32a22a423c71c8dc479cdbd5d6de98772431b10d
13 files changed