I think this was already the intention, but DeadMachineInstructionElim
was accidentally tracking the liveness of reserved registers. Now,
instructions with reserved defs are never deleted.
This prevents the call stack adjustment instructions from getting
deleted when enabling register masks.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150116 91177308-0d34-0410-b5e6-96231b3b80d8