add -r option to docker/build.sh for executing as root
Add arm64 dockerfile
add support for 8.1 SDK
Merge pull request #375 from joshuawarner32/docker-arm64

Docker arm64
Merge pull request #376 from joshuawarner32/8.1-ios-sdk

add support for 8.1 SDK
split low/high register mask in OperandMask
begin converting to setLowHighRegisterMasks
rename RegisterMask to BoundedRegisterMask
remove unused arm utilities / constants
typedef RegisterMask
remove old 32-bit registerMask stuff
typdef Register
typedef Register and RegisterMask in arm
make RegisterMask a class
begin renaming lir:: types
finish renaming lir:: types (fixup arm)
rename lir::Register to lir::RegisterPair
make Register a class
add back NoRegister and remove some implicit int->Register casts
transition x86 registers to Register instances