Factor out PointerIdentity.
Add implementations of Target, TargetMachine and TargetDataLayout.
YARD error fixes.
Properly initialize native/all targets.
Deprecate LLVM.init_x86 in favor of new LLVM::Target API.
Update PassManagers to be compatible with both ExecutionEngine and TargetMachine.
Merge remote-tracking branch 'whitequark/ptrid'
Merge whitequark/target (and make ARM test conditional.)