ENH: Macro should be scriptable

Source/cmMacroCommand.h

@@ -67,6 +67,11 @@ public:
    */
   virtual bool IsInherited() {return true;}
 
+  /**
+   * This determines if the command is invoked when in script mode.
+   */
+  virtual bool IsScriptable() { return true; }
+
   /**
    * The name of the command as specified in CMakeList.txt.
    */