[lld] [PAC][lld][ELF] Use PAC instructions in PLT header with `-z pac-plt` (PR #116334)

[Anton Korobeynikov via llvm-commits]

asl wrote:

> What is the compatibility story about pacibsp and does GNU ld (which supports the option as well) decides to do something similar?

Tagging @smithp35 

My understanding is that pac-plt changes never made it to glibc, right?

https://github.com/llvm/llvm-project/pull/116334