[clang] [clang] Constant evaluation support for `__builtin_fmax{,f,l}` and `__builtin_fmin{,f,l}` (PR #225824)

[Lucas Mellone via cfe-commits]

lknknm wrote:

I am drafting this PR until we have a clear direction of where to go with the constexpr builtins.

https://github.com/llvm/llvm-project/pull/225824