[llvm] [AArch64][CodeGen] Add patterns for +lsfe atomic stores (PR #131174)

[David Green via llvm-commits]

davemgreen wrote:

> I wonder whether we should add the tests anyway, to check that they _don't_ lower to `ST[F]ADD`?

Yeah they might be useful to keep. The last few times this has come up there has been a suggestion to add a comment somewhere to explain why we don't generate them too.

https://github.com/llvm/llvm-project/pull/131174