[lld] [lld][AArch64][ELF][PAC] Support `.relr.auth.dyn` section (PR #96496)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay requested changes to this pull request.

`.rela.dyn` is currently created outside of the `config->hasDynSymTab` condition.
In relocatable links, `.rela.dyn` will be discarded by `removeUnusedSyntheticSections`.
The reverted `.relr.auth.dyn` patch incorrectly retained the empty `.relr.dyn`.

I think we should suppress the creation of `.rela.dyn` in the first place.
I will try updating `createSyntheticSections`.

The `!config->relocatable` condition in `removeUnusedSyntheticSections` in this PR can then be dropped.


https://github.com/llvm/llvm-project/pull/96496