[lld] [llvm] [lld][AArch64][Build Attributes] Add support for AArch64 Build Attributes (PR #147970)

[Peter Smith via llvm-commits]

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

I've spotted another couple of bits that can be removed (forward declaration and whitespace).

I've set approved (assuming changes have been made). Please wait for @MaskRay approval before merging.

https://github.com/llvm/llvm-project/pull/147970