Reapply "[SystemZ] Bugfix in expansion of memmem operations."

The new test case showed that the NoPHIs flag needs to be cleared.

Original commit message:

[SystemZ] Bugfix in expansion of memmem operations.

Since NC, OC, and XC clobber CC, the EXRL_Pseudo targeting these must also be
marked to do so.

Original patch by uweigand.

Reviewed by: uweigand

Differential Revision: https://reviews.llvm.org/D150251

Fixes: https://github.com/llvm/llvm-project/issues/62572