[llvm] [AArch64] Emit .arch and .arch_extension during assembly to textual asm (PR #138433)

[Peter Smith via llvm-commits]

https://github.com/smithp35 approved this pull request.

LGTM too.

I guess this can in theory affect ARM as well, although the .arch+<features> is likely not well supported in ARM either.

https://github.com/llvm/llvm-project/pull/138433