[llvm] [X86] Recognize VPXORDZrr as a zero-idiom on Znver4 (PR #108314)

[Simon Pilgrim via llvm-commits]

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

LGTM as a stopgap - after this has landed, please can you add a test file for #108157 as well? We can keep #108157 open until we have the real fix.

https://github.com/llvm/llvm-project/pull/108314