Adding support for some missing intrinsics:
_castf32_u32, _castf64_u64, _castu32_f32, _castu64_f64
There's an unofficial agreement that new x86 intrinsics should have doxygen comments - someday we'll get around to adding them to the existing ones as well.....
Shouldn't the unsigned long long cases be hidden by x86_64 wrappers?
32-bit target tests?
icc doesn't restrict this to 64-bit targets. On 64-bit targets it corresponds to movq, but on other targets we can just lower to a 64-bit store and two 32-bit loads in the worst case.