Shouldn't be too hard to add later, since they're mostly just swizzles onto the existing instructions, and LLVM already has good support for registering slightl

Shouldn't be too hard to add later, since they're mostly just swizzles onto the existing instructions, and LLVM already has good support for registering slightly different versions of a target (subtargeting). For now, I'm targeting the plain-jane MOS chip, since it's the buggiest and least capable, and thus the most difficult.