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

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gonzalobg wrote:

I emailed the gcc mailing list and opened an RFC and got no objections for now.

I had a call with Matthew Malcomson.
He asked: why does clang add `..._fetch`-versions (returning the new value) of all the atomics builtins?
TBH I only added them due to inertia and don't know the answer.
@efriedma-quic @jyknight @jdoerfert do you know?

I've removed these for now since they are not needed for libc++.
Happy to add them in a subsequent PR if there is a need.

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