Jit IR

Initial implementation of an "IR"  (intermediate representation) for the recompiler. May allow some advanced inlining and reordering optimizations in the JIT over time.

Does not seem to affect performance much if at all, at the moment.

Tested on ARM and x86/x64. Want this in before I start working on the ARM64 JIT.
Blah.  Well, it's not great but we could use a `#define` for it at least...

-[Unknown]