MO_MachineRegister, we no longer distinguish Virtual vs. Machine registers
externally, they're ALL registers, all equal.
Registers are only differentiated whether they are >=
MRegisterInfo::FirstVirtual or not.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4823 91177308-0d34-0410-b5e6-96231b3b80d8