Remove FormConcept::menus_ from Linux builds

Author: ProgramMax

Code/maxGUI/FormConcept.hpp

@@ -124,7 +124,9 @@ namespace maxGUI
 		#endif
 
 		std::vector<std::unique_ptr<Control>> controls_;
+#if defined(MAX_PLATFORM_WINDOWS)
 		std::vector<std::unique_ptr<Menu>> menus_;
+#endif
 
 	};