Long doubles are always at least 80 bits wide in memory and it suffices
if we can address these 80 bits, to mark the long double as NAN at the
end of an MMX instruction, so the additional magic using conditional
types is unnecessary.
This implements almost all instructions related to the FPU, including
all MMX instructions as well.
A lot of these were copied and adjusted from the SoftCPU implementation.
The next big milestone would be QNan detection and ShadowValue handling.
