[SystemZ] Bugfix: Don't add CC twice to new three-address instruction.

Since BuildMI() automatically adds the implicit operands for a new instruction,
adding the old instructions CC operand resulted in that there were two CC imp-def
operands, where only one was marked as dead. This caused buildSchedGraph() to
miss dependencies on the CC reg.

Review by Ulrich Weigand

llvm-svn: 254714