gtk: Add get_type() function declarations for private objects

I'm adding a bunch of fixes for gcc complaining about
-Wmissing-declarations.

This set of patches makes private classes in gtk/*.c that use
G_DEFINE_TYPE() safe by adding definitions for the get_type() function
that can't be made static.

gtk/gtkcellrendereraccel.c

@@ -579,6 +579,8 @@ struct _GtkCellEditableEventBox
   gboolean editing_canceled;
 };
 
+GType _gtk_cell_editable_event_box_get_type (void);
+
 G_DEFINE_TYPE_WITH_CODE (GtkCellEditableEventBox, _gtk_cell_editable_event_box, GTK_TYPE_EVENT_BOX, { \
     G_IMPLEMENT_INTERFACE (GTK_TYPE_CELL_EDITABLE, _gtk_cell_editable_event_box_cell_editable_init)   \
       })

gtk/gtkfilechooserdefault.c

@@ -454,6 +454,8 @@ typedef struct {
 
 static void shortcuts_pane_model_filter_drag_source_iface_init (GtkTreeDragSourceIface *iface);
 
+GType _shortcuts_pane_model_filter_get_type (void);
+
 G_DEFINE_TYPE_WITH_CODE (ShortcutsPaneModelFilter,
 			 _shortcuts_pane_model_filter,
 			 GTK_TYPE_TREE_MODEL_FILTER,

gtk/gtkpango.c

@@ -49,6 +49,8 @@ struct _GtkFillLayoutRendererClass
   PangoRendererClass parent_class;
 };
 
+GType _gtk_fill_layout_renderer_get_type (void);
+
 G_DEFINE_TYPE (GtkFillLayoutRenderer, _gtk_fill_layout_renderer, PANGO_TYPE_RENDERER)
 
 static void

gtk/gtkprintbackend.c

@@ -103,6 +103,8 @@ struct _GtkPrintBackendModuleClass
   GTypeModuleClass parent_class;
 };
 
+GType _gtk_print_backend_module_get_type (void);
+
 G_DEFINE_TYPE (GtkPrintBackendModule, _gtk_print_backend_module, G_TYPE_TYPE_MODULE)
 #define GTK_TYPE_PRINT_BACKEND_MODULE      (_gtk_print_backend_module_get_type ())
 #define GTK_PRINT_BACKEND_MODULE(module)   (G_TYPE_CHECK_INSTANCE_CAST ((module), GTK_TYPE_PRINT_BACKEND_MODULE, GtkPrintBackendModule))

gtk/gtkscalebutton.c

@@ -1423,6 +1423,8 @@ static gboolean	gtk_scale_button_scale_press   (GtkWidget      *widget,
 static gboolean gtk_scale_button_scale_release (GtkWidget      *widget,
                                                 GdkEventButton *event);
 
+GType           _gtk_scale_button_scale_get_type (void);
+
 G_DEFINE_TYPE (GtkScaleButtonScale, _gtk_scale_button_scale, GTK_TYPE_SCALE)
 
 static void

gtk/gtktextdisplay.c

@@ -121,6 +121,8 @@ struct _GtkTextRendererClass
   PangoRendererClass parent_class;
 };
 
+GType _gtk_text_renderer_get_type (void);
+
 G_DEFINE_TYPE (GtkTextRenderer, _gtk_text_renderer, PANGO_TYPE_RENDERER)
 
 static void

gtk/gtkthemingengine.c

@@ -208,6 +208,8 @@ struct GtkThemingModuleClass
 #define GTK_THEMING_MODULE(o)    (G_TYPE_CHECK_INSTANCE_CAST ((o), GTK_TYPE_THEMING_MODULE, GtkThemingModule))
 #define GTK_IS_THEMING_MODULE(o) (G_TYPE_CHECK_INSTANCE_TYPE ((o), GTK_TYPE_THEMING_MODULE))
 
+GType gtk_theming_module_get_type (void);
+
 G_DEFINE_TYPE (GtkThemingModule, gtk_theming_module, G_TYPE_TYPE_MODULE);
 
 static void