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

[Sam Elliott via llvm-commits]

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

LGTM. Please wait for one of the tagged reviewers to also chime in, they're all at Arm.

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