[X86] Check Subtarget.hasSSE3() before calling shouldUseHorizontalOp and emitting X86ISD::FHADD in LowerUINT_TO_FP_i64.

This was a regression from r375341.

Fixes PR43729.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375381 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed