[SystemZ] Add LOC and LOCG

As with the stores, these instructions can trap when the condition is false,
so they are only used for things like (cond ? x : *ptr).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187112 91177308-0d34-0410-b5e6-96231b3b80d8