[llvm] [SystemZ] Don't lower float/double ATOMIC_[LOAD|STORE] to [LOAD|STORE] (PR #75879)

[Ulrich Weigand via llvm-commits]

https://github.com/uweigand commented:

Looks generally good to me, but see a couple of questions inline with the test case.

https://github.com/llvm/llvm-project/pull/75879