Make deviare hook only active in _WIN64 case.

Crashed in AC4 with this enabled in debug x32.
Right now, it's only valid for WatchDogs and debug in x64, needs x32 libraries if we decide to use it.
Fix bugs with generating round_z, round_ne.

These were using just Round for both, which is incorrect.
round_z is to use Trunc, round_ne uses Round.

Also removed the unrolling of the instruction, so that it's fewer lines and more clearly matches original ASM.

Tested in AC4, generates right code.