[clang] [Clang] Fix clang to emit llvm-ir for fadd/fsub atomics (PR #162679)

[Tomas Matheson via cfe-commits]

tmatheson-arm wrote:

If this is to support LSFE features, we likely want to stick with the CAS loops unless that feature is available.

What do `fmax/fmin` lower to with/without LSFE?

https://github.com/llvm/llvm-project/pull/162679