[llvm] [SystemZ] Replace SELRMux with COPY in case of identical operands. (PR #125108)

[Ulrich Weigand via llvm-commits]

https://github.com/uweigand approved this pull request.

Huh, interesting case.  Would be good to fix the formatting issue, otherwise LGTM.

https://github.com/llvm/llvm-project/pull/125108