[TargetLowering] expandFP_TO_UINT - avoid FPE due to out of range conversion (PR17686)

PR17686 demonstrates that for some targets FP exceptions can fire in cases where the FP_TO_UINT is expanded using a FP_TO_SINT instruction.

The existing code converts both the inrange and outofrange cases using FP_TO_SINT and then selects the result, this patch changes this for 'strict' cases to pre-select the FP_TO_SINT input and the offset adjustment.

The X87 cases don't need the strict flag but generates much nicer code with it....

Differential Revision: https://reviews.llvm.org/D53794

llvm-svn: 348251