[clang] [Clang] `constexpr` builtin floating point classification / comparison functions (PR #94118)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

The changes generally LGTM, but should come with a release note. Do you think there's a reasonable way to share code between the two constant expression interpreters in this case?

https://github.com/llvm/llvm-project/pull/94118