[clang] [flang] [llvm] [C++23] [CLANG] Adding C++23 constexpr math functions: fmin, fmax and frexp. (PR #88978)

[Hubert Tong via cfe-commits]

hubert-reinterpretcast wrote:

> Yes, I have tried limiting it to `LibBuiltin` but the addition of `FrexpF16F128` led me to add it `Builtin` too.

I believe that FrexpF16F128 only has the `__builtin_`-prefixed versions. That would mean that it does not need to be "constexpr since" (just plain "constexpr").

https://github.com/llvm/llvm-project/pull/88978