Fix this warning:

DAGCombiner.cpp: In member function 'llvm::SDOperand<unnamed>::DAGCombiner::visitOR(llvm::SDNode*)':
DAGCombiner.cpp:1608: warning: passing negative value '-0x00000000000000001' for argument 1 to 'llvm::SDOperand llvm::SelectionDAG::getConstant(uint64_t, llvm::MVT::ValueType, bool)'

oiy.

llvm-svn: 38458