[lld] [lld] Add target support for SystemZ (s390x) (PR #75643)

[Ulrich Weigand via llvm-commits]

uweigand wrote:

> > you should check current mainline, which has some fixes against the latest published version
> 
> Can you ask the team to vendor a new release? The last published pdf was Nov '21.

Version 1.6.1 is now out: https://github.com/IBM/s390x-abi/releases/tag/v1.6.1 - thanks @aarnez !

https://github.com/llvm/llvm-project/pull/75643