Fix wxGTK build with glib < 2.32 and streamline the code a bit

Define g_signal_handlers_disconnect_by_data() if it's not available,
i.e. when using glib older than 2.32 where it was added, to fix the
build under old systems such as CentOS 6 broken by the changes of
8278f7b618 (see #18084).

Also use it elsewhere instead of g_signal_handlers_disconnect_matched()
as it's more readable.

Closes https://github.com/wxWidgets/wxWidgets/pull/760

src/gtk/menu.cpp

@@ -808,8 +808,7 @@ wxMenu::~wxMenu()
     // Destroying a menu generates a "hide" signal even if it's not shown
     // currently, so disconnect it to avoid dummy wxEVT_MENU_CLOSE events
     // generation.
-    g_signal_handlers_disconnect_matched(m_menu,
-        GSignalMatchType(G_SIGNAL_MATCH_DATA), 0, 0, NULL, NULL, this);
+    g_signal_handlers_disconnect_by_data(m_menu, this);
 
     if (m_owner)
     {
@@ -993,8 +992,7 @@ wxMenuItem *wxMenu::DoRemove(wxMenuItem *item)
 
     GtkWidget * const mitem = item->GetMenuItem();
 
-    g_signal_handlers_disconnect_matched(mitem,
-        GSignalMatchType(G_SIGNAL_MATCH_DATA), 0, 0, NULL, NULL, item);
+    g_signal_handlers_disconnect_by_data(mitem, item);
 
 #ifdef __WXGTK3__
     gtk_menu_item_set_submenu(GTK_MENU_ITEM(mitem), NULL);