[clang] [compiler-rt] [llvm] [clang] builtins for atomicrmw fminmax/_num (PR #187139)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

I'm not sure what patterns are most commonly used in practice, off the top of my head.  GitHub shows 12k hits for `__atomic_add_fetch` (including a couple in libc++).

I'm fine with excluding the variants for new ops, though.

https://github.com/llvm/llvm-project/pull/187139