[lld] [lld][AArch64][ELF][PAC] Support AUTH relocations and AUTH ELF marking (PR #72714)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> @MaskRay Would be glad to see your feedback on the changes

Apologies for the delay. I think the latest update is really close. I've made several comments. The primary ones are:

* processAux should be simplified
* how `finalizeAddressDependentContent` should do the fixup.
* an unneeded `template`

https://github.com/llvm/llvm-project/pull/72714