[TargetLowering] In expandFP_TO_UINT, add proper extend or truncate for the...

[TargetLowering] In expandFP_TO_UINT, add proper extend or truncate for the condition to feed the DstVT select.

Previously, for vectors we created a vselect with a condition that
didn't match what the target wanted according to getSetCCResultType.

To make up for this, X86 had a special DAG combine to detect if
the condition was all sign bits and then insert its own truncate
or extend. By adding the extend/truncate here explicitly we can
avoid that.