Factor out global generator ComputeTargetDepends method

Put the global dependency analysis in its own method so individual
generators can hook into this point.

Source/cmGlobalGenerator.cxx

@@ -863,19 +863,10 @@ void cmGlobalGenerator::Generate()
     }
 
   // Compute the inter-target dependencies.
-  {
+  if(!this->ComputeTargetDepends())
-  cmComputeTargetDepends ctd(this);
-  if(!ctd.Compute())
     {
     return;
     }
-  std::vector<cmTarget*> const& targets = ctd.GetTargets();
-  for(std::vector<cmTarget*>::const_iterator ti = targets.begin();
-      ti != targets.end(); ++ti)
-    {
-    ctd.GetTargetDirectDepends(*ti, this->TargetDependencies[*ti]);
-    }
-  }
 
   // Create a map from local generator to the complete set of targets
   // it builds by default.
@@ -907,6 +898,23 @@ void cmGlobalGenerator::Generate()
   this->CMakeInstance->UpdateProgress("Generating done", -1);
 }
 
+//----------------------------------------------------------------------------
+bool cmGlobalGenerator::ComputeTargetDepends()
+{
+  cmComputeTargetDepends ctd(this);
+  if(!ctd.Compute())
+    {
+    return false;
+    }
+  std::vector<cmTarget*> const& targets = ctd.GetTargets();
+  for(std::vector<cmTarget*>::const_iterator ti = targets.begin();
+      ti != targets.end(); ++ti)
+    {
+    ctd.GetTargetDirectDepends(*ti, this->TargetDependencies[*ti]);
+    }
+  return true;
+}
+
 //----------------------------------------------------------------------------
 bool cmGlobalGenerator::CheckTargets()
 {

Source/cmGlobalGenerator.h

@@ -275,6 +275,8 @@ protected:
   void SetLanguageEnabledMaps(const char* l, cmMakefile* mf);
   void FillExtensionToLanguageMap(const char* l, cmMakefile* mf);
 
+  virtual bool ComputeTargetDepends();
+
   virtual bool CheckALLOW_DUPLICATE_CUSTOM_TARGETS();
 
   bool CheckTargets();