[DAGCombiner] Enable sdiv(x.y) -> udiv(x,y) combine for vectors

SelectionDAG::SignBitIsZero (via SelectionDAG::computeKnownBits) has supported vectors since rL280927

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@285118 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed