JIT64: merge floating point comparisons with branches where possible

This is kind of a WIP; it's a huge hunk of code and rather a mess at the moment, though I'm not sure it can be simplified too much.

Patterned (kinda) after the integer equivalent.

I hate NaNs with the burning fire of a thousand quasars.

~3-4% speed boost on Sonic Colors from a quick test (going by max turbo speed at the menu).