Enable gcc attribute suggestion warnings

Adding `final` can allow gcc to devirtualize a call.  Request compiler
warnings wherever `final` would improve this.  As of this writing, there
are no places where `final` would be helpful and would also be wrong, so
this is enabled everywhere.

SConstruct

@@ -2710,6 +2710,8 @@ constexpr literal_as_type<T, v...> operator""_literal_as_type();
 		'-Wduplicated-branches',
 		'-Wduplicated-cond',
 		'-Wsuggest-attribute=noreturn',
+		'-Wsuggest-final-types',
+		'-Wsuggest-override',
 		'-Wlogical-op',
 		'-Wold-style-cast',
 		'-Wredundant-decls',

common/include/editor/editor.h

@@ -520,7 +520,7 @@ extern grs_subcanvas _canv_editor_game;		//the game on the editor screen
 extern grs_canvas *Canv_editor;			//the editor screen
 extern grs_subcanvas *const Canv_editor_game; //the game on the editor screen
 
-struct editor_dialog : UI_DIALOG
+struct editor_dialog final : UI_DIALOG
 {
 	using UI_DIALOG::UI_DIALOG;
 	std::array<std::unique_ptr<UI_GADGET_BUTTON>, 9> pad_goto;

common/main/game.h

@@ -156,7 +156,7 @@ enum class StereoFormat : uint8_t
 #ifdef dsx
 namespace dsx {
 
-struct game_window : window
+struct game_window final : window
 {
 	using window::window;
 	virtual window_event_result event_handler(const d_event &) override;

common/main/newmenu.h

@@ -553,7 +553,7 @@ namespace dcx {
 
 int nm_messagebox_str(menu_title title, const nm_messagebox_tie &tie, menu_subtitle str);
 
-struct messagebox_newmenu :
+struct messagebox_newmenu final :
 	std::array<newmenu_item, nm_messagebox_tie::maximum_arity>,
 	newmenu
 {