Move all getTargetNode() out of SelectionDAG.h into SelectionDAG.cpp. This
prevents them from being inlined.
Change getTargetNode() so they return SDNode * instead of SDOperand to prevent
copying. It should also help compilation speed.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26083 91177308-0d34-0410-b5e6-96231b3b80d8