'Gimme whatever register' in the DSL

[kozross]

It'd be nice if you could have a construction in the DSL that means 'gimme a register, I don't care which specific one', similar to what you can do with extended inline asm in GCC and Clang. This is mostly useful for GPRs, as keeping track of this manually is really tedious. SIMD registers aren't as bad, but it'd be nice for those too.