Don't replace the old Ordering object with a new one; just clear()

the old one.

llvm-svn: 106284

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -833,8 +833,7 @@ void SelectionDAG::clear() {
   EntryNode.UseList = 0;
   AllNodes.push_back(&EntryNode);
   Root = getEntryNode();
-  delete Ordering;
-  Ordering = new SDNodeOrdering();
+  Ordering->clear();
   DbgInfo->clear();
 }