[SystemZ] Bugfix: check CC reg liveness in SystemZShortenInst.

[SystemZ] Bugfix: check CC reg liveness in SystemZShortenInst.

The following instruction shortening transformations would introduce a
definition of the CC reg, so therefore liveness of CC reg must be checked:

WFADB -> ADBR
WFSDB -> SDBR

Also add the CC reg implicit def operand to the MI in case of change of opcode.

Reviewed by Ulrich Weigand.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249665 91177308-0d34-0410-b5e6-96231b3b80d8