[lld] [LLD][ELF][AArch64] Add BTI Aware long branch thunks (PR #108989)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Thanks for the patch. I am back from vacation and will check this shortly.

FYI: I plan to replace `config->x` with `ctx.arg.x` to move toward the goal to eliminate the global states. It should require minimal changes to this patch.

https://github.com/llvm/llvm-project/pull/108989