(temp): split low/high register mask in OperandMask
(temp): begin converting to setLowHighRegisterMasks
(temp): rename RegisterMask to BoundedRegisterMask
(temp): remove unused arm utilities / constants
(temp): typedef RegisterMask
(temp): remove old 32-bit registerMask stuff
(temp): typdef Register
(temp): typedef Register and RegisterMask in arm
(temp): make RegisterMask a class
(temp): begin renaming lir:: types
(temp): finish renaming lir:: types (fixup arm)
(temp): rename lir::Register to lir::RegisterPair
(temp): make Register a class
(temp): add back NoRegister and remove some implicit int->Register casts
(temp): transition x86 registers to Register instances
(temp): get rid of implicit Register casts
(temp): make BoundedRegisterMask a subclass of RegisterMask