SelectionDAG and it has since bitrotted. Remove the copy from SelectionDAG.
Next, remove the constant folding piece of DAGCombiner::SimplifySetCC into
a new FoldSetCC method which can be used by getNode() and SimplifySetCC.
This fixes obscure bugs.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@30952 91177308-0d34-0410-b5e6-96231b3b80d8