ENH: Support linking to shared libs with dependent libs

- Split IMPORTED_LINK_LIBRARIES into two parts:
      IMPORTED_LINK_INTERFACE_LIBRARIES
      IMPORTED_LINK_DEPENDENT_LIBRARIES
  - Add CMAKE_DEPENDENT_SHARED_LIBRARY_MODE to select behavior
  - Set mode to LINK for Darwin (fixes universal binary problem)
  - Update ExportImport test to account for changes

Source/cmTarget.h

@@ -35,9 +35,13 @@ struct cmTargetLinkInformationMap:
   ~cmTargetLinkInformationMap();
 };
 
-struct cmTargetLinkInterface: public std::vector<std::string>
+struct cmTargetLinkInterface
 {
-  typedef std::vector<std::string> derived;
+  // Libraries listed in the interface.
+  std::vector<std::string> Libraries;
+
+  // Shared library dependencies needed for linking on some platforms.
+  std::vector<std::string> SharedDeps;
 };
 
 struct cmTargetLinkInterfaceMap:
@@ -218,11 +222,6 @@ public:
 
   bool IsImported() const {return this->IsImportedTarget;}
 
-  /** Get link libraries for the given configuration of an imported
-      target.  */
-  std::vector<std::string> const*
-  GetImportedLinkLibraries(const char* config);
-
   /** Get the library interface dependencies.  This is the set of
       libraries from which something that links to this target may
       also receive symbols.  Returns 0 if the user has not specified
@@ -487,7 +486,7 @@ private:
     std::string Location;
     std::string SOName;
     std::string ImportLibrary;
-    std::vector<std::string> LinkLibraries;
+    cmTargetLinkInterface LinkInterface;
   };
   typedef std::map<cmStdString, ImportInfo> ImportInfoMapType;
   ImportInfoMapType ImportInfoMap;