[DirectedGraph]: Add setTargetNode member function

Summary:Add the setTargetNode member function to class DGEdge.
Authored By:etiotto
Reviewer:bmahjour, Whitney, jdoerfert, Meinersbur, fhahn, kbarton,
dmgreen
Reviewed By:Meinersbur
Subscribers:dexonsmith, kristina, llvm-commits
Tag:LLVM
Differential Revision:https://reviews.llvm.org/D68474

llvm/include/llvm/ADT/DirectedGraph.h

@@ -48,6 +48,9 @@ public:
         static_cast<const DGEdge<NodeType, EdgeType> &>(*this).getTargetNode());
   }
 
+  /// Set the target node this edge connects to.
+  void setTargetNode(const NodeType &N) { TargetNode = N; }
+
 protected:
   // As the default implementation use address comparison for equality.
   bool isEqualTo(const EdgeType &E) const { return this == &E; }