[llvm] [AArch64] Emit ST<OP> instruction when the return value has no use. (PR #72887)

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ktkachov-arm wrote:

Thanks for validating :) FWIW I think it would make sense to add a comment to the LLVM source explaining this nuance so that future generations don't try to replay this (non-obvious) change. The GCC source for this instruction does contain a comment to that effect

https://github.com/llvm/llvm-project/pull/72887