[LegalizeTypes] When expanding the integer result of LLROUND/LLRINT, also call...

[LegalizeTypes] When expanding the integer result of LLROUND/LLRINT, also call GetSoftenedFloat if the floating point input needs to be softened.

Before this we were emitting a bitcast to integer from the lowering
code that itself will need to be legalized. By calling
GetSoftenedFloat we get the integer conversion in one step without
needing to relegalize a bitcast.