The def operand of the new LG/LD should have the old def operands
flags and subreg index.
New test: test/CodeGen/SystemZ/fold-memory-op-impl.ll
Review: Ulrich Weigand
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298341 91177308-0d34-0410-b5e6-96231b3b80d8