[libc++] update fetch min/max apis to use builtins in compilers that have them

#186694 implements P0493 min/max APIs in libc++.
This initial implementation uses compare-exchange loops since these are properly supported by all targets.
This issue tracks optimizing this implementation to use builtins in compilers that have them available and correctly implemented.

Start with #186694 and locate the libc++ implementation of the P0493 min/max APIs. Compare the existing compare-exchange loops with compiler builtins available on supported targets, then verify that supported compilers use the builtins while other targets retain the portable behavior.

Written by the indexing model from the issue text.