[SystemZ] Use XC for a memset of 0


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190130 91177308-0d34-0410-b5e6-96231b3b80d8
[mips][msa] Made the InstrItinClass argument optional since it is always NoItinerary at the moment.

No functional change



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190131 91177308-0d34-0410-b5e6-96231b3b80d8