[SelectionDAG] Make DAGTypeLegalizer::PromoteSetCCOperands handle SETEQ/SETNE correct...

[SelectionDAG] Make DAGTypeLegalizer::PromoteSetCCOperands handle SETEQ/SETNE correctly for vector types.

The code was using getValueSizeInBits and combining with the result of a call to DAG.ComputeNumSignBits. But for vector types getValueSizeInBits returns the width of the full vector while ComputeNumSignBits is going to give a number no larger than the width of a single element. So we should be using getScalarValueSizeInBits to get the element width.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@323583 91177308-0d34-0410-b5e6-96231b3b80d8