meta: Only declare types when generating gir files

Some types were declared in the public headers so that g-ir-scanner
could resolve the types. This caused warnings when using
-Wredundant-decls, so only redeclare them for the gir scanner.

src/meta/meta-backend.h

@@ -34,6 +34,10 @@
 typedef struct _MetaBackend        MetaBackend;
 typedef struct _MetaBackendClass   MetaBackendClass;
 
+#ifdef __GI_SCANNER__
+GType meta_backend_get_type (void);
+#endif
+
 MetaBackend * meta_get_backend (void);
 
 void meta_backend_set_keymap (MetaBackend *backend,

src/meta/meta-monitor-manager.h

@@ -54,7 +54,9 @@ MetaMonitorSwitchConfigType meta_monitor_manager_get_switch_config (MetaMonitorM
 
 gint meta_monitor_manager_get_display_configuration_timeout (void);
 
+#ifdef __GI_SCANNER__
 /* Re-declaration of parent type for introspection */
 GType meta_dbus_display_config_skeleton_get_type (void) G_GNUC_CONST;
+#endif
 
 #endif /* META_MONITOR_MANAGER_H */

src/meta/meta-startup-notification.h

@@ -27,7 +27,9 @@
 typedef struct _MetaStartupNotification MetaStartupNotification;
 typedef struct _MetaStartupSequence MetaStartupSequence;
 
+#ifdef __GI_SCANNER__
 GType         meta_startup_notification_get_type      (void);
+#endif
 
 /**
  * meta_startup_notification_get_sequences: (skip)
@@ -37,7 +39,9 @@ GSList *      meta_startup_notification_get_sequences (MetaStartupNotification *
 MetaLaunchContext *
              meta_startup_notification_create_launcher (MetaStartupNotification *sn);
 
+#ifdef __GI_SCANNER__
 GType         meta_startup_sequence_get_type          (void);
+#endif
 
 const char * meta_startup_sequence_get_id             (MetaStartupSequence *sequence);
 gboolean     meta_startup_sequence_get_completed      (MetaStartupSequence *sequence);