[llvm] [AArch64][CodeGen] Add +lsfe atomicrmw tests where the result is unused. (PR #132022)

[Jonathan Thackray via llvm-commits]

https://github.com/jthackray approved this pull request.

LGTM; should help us when we revisit this in future

https://github.com/llvm/llvm-project/pull/132022