[LegalizeTypes] Add SoftenFloatResult support for STRICT_SINT_TO_FP/STRICT_UINT_TO_FP

Some target like arm/riscv with soft-float will have compiling crash when using -fno-unsafe-math-optimization option.
This patch will add the missing strict FP support to SoftenFloatRes_XINT_TO_FP.

Differential Revision: https://reviews.llvm.org/D72277