ENH: Improve link line generation for static library cycles.

- Move Tarjan algorithm from cmComputeTargetDepends
    into its own class cmComputeComponentGraph
  - Use cmComputeComponentGraph to identify the component DAG
    of link dependencies in cmComputeLinkDepends
  - Emit non-trivial component members more than once but always
    in a contiguous group on the link line

Source/cmComputeComponentGraph.h

@@ -0,0 +1,87 @@
+/*=========================================================================
+
+  Program:   CMake - Cross-Platform Makefile Generator
+  Module:    $RCSfile$
+  Language:  C++
+  Date:      $Date$
+  Version:   $Revision$
+
+  Copyright (c) 2002 Kitware, Inc., Insight Consortium.  All rights reserved.
+  See Copyright.txt or http://www.cmake.org/HTML/Copyright.html for details.
+
+     This software is distributed WITHOUT ANY WARRANTY; without even
+     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+     PURPOSE.  See the above copyright notices for more information.
+
+=========================================================================*/
+#ifndef cmComputeComponentGraph_h
+#define cmComputeComponentGraph_h
+
+#include "cmStandardIncludes.h"
+
+#include "cmGraphAdjacencyList.h"
+
+#include <stack>
+
+/** \class cmComputeComponentGraph
+ * \brief Analyze a graph to determine strongly connected components.
+ *
+ * Convert a directed graph into a directed acyclic graph whose nodes
+ * correspond to strongly connected components of the original graph.
+ *
+ * We use Tarjan's algorithm to enumerate the components efficiently.
+ * An advantage of this approach is that the components are identified
+ * in a topologically sorted order.
+ */
+class cmComputeComponentGraph
+{
+public:
+  // Represent the graph with an adjacency list.
+  typedef cmGraphNodeList NodeList;
+  typedef cmGraphAdjacencyList Graph;
+
+  cmComputeComponentGraph(Graph const& input);
+  ~cmComputeComponentGraph();
+
+  /** Get the adjacency list of the component graph.  */
+  Graph const& GetComponentGraph() const
+    { return this->ComponentGraph; }
+  NodeList const& GetComponentGraphEdges(int c) const
+    { return this->ComponentGraph[c]; }
+
+  /** Get map from component index to original node indices.  */
+  std::vector<NodeList> const& GetComponents() const
+    { return this->Components; }
+  NodeList const& GetComponent(int c) const
+    { return this->Components[c]; }
+
+  /** Get map from original node index to component index.  */
+  std::vector<int> const& GetComponentMap() const
+    { return this->TarjanComponents; }
+
+private:
+  void TransferEdges();
+
+  Graph const& InputGraph;
+  Graph ComponentGraph;
+
+  // Tarjan's algorithm.
+  struct TarjanEntry
+  {
+    int Root;
+    int VisitIndex;
+  };
+  int TarjanWalkId;
+  std::vector<int> TarjanVisited;
+  std::vector<int> TarjanComponents;
+  std::vector<TarjanEntry> TarjanEntries;
+  std::stack<int> TarjanStack;
+  int TarjanIndex;
+  void Tarjan();
+  void TarjanVisit(int i);
+
+  // Connected components.
+  std::vector<NodeList> Components;
+};
+
+#endif