SINT_TO_FP libcall plus additional operations:
it might as well be a direct UINT_TO_FP libcall.
So only turn it into an SINT_TO_FP if the target
has special handling for SINT_TO_FP.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53461 91177308-0d34-0410-b5e6-96231b3b80d8