ENH: Keep only FinalPass commands in memory

In cmMakefile we save all invoked commands so that FinalPass can be
called on them later.  Most commands have no final pass, so we should
keep only the few that do.

Source/cmLoadCommandCommand.cxx

@@ -68,6 +68,8 @@ public:
    * writing to the cache can be done.
    */
   virtual void FinalPass();
+  virtual bool HasFinalPass() const
+    { return this->info.FinalPass? true:false; }
 
   /**
    * The name of the command as specified in CMakeList.txt.