gtk.cfg: Enhance some gtk_signal_* functions

Add deprecation warnings and missing configurations for some of the
gtk_signal_* functions.
References:
https://developer.gnome.org/gtk2/stable/gtk2-Signals.html
https://developer.gimp.org/api/2.0/gtk/gtk-Signals.html

cfg/gtk.cfg

@@ -8166,21 +8166,67 @@
     <leak-ignore/>
     <noreturn>false</noreturn>
   </function>
+  <!-- #define gtk_signal_connect(object,name,func,func_data) -->
+  <function name="gtk_signal_connect">
+    <noreturn>false</noreturn>
+    <warn severity="style" alternatives="g_signal_connect" reason="Obsolete"/>
+    <arg nr="1"/>
+    <arg nr="2"/>
+    <arg nr="3"/>
+    <arg nr="4"/>
+  </function>
+  <!-- gulong gtk_signal_connect_full (GtkObject *object,
+                                       const gchar *name,
+                                       GCallback func,
+                                       GtkCallbackMarshal unsupported,
+                                       gpointer data,
+                                       GDestroyNotify destroy_func,
+                                       gint object_signal,
+                                       gint after); -->
   <function name="gtk_signal_connect_full">
     <leak-ignore/>
     <noreturn>false</noreturn>
+    <returnValue type="gulong"/>
+    <warn severity="style" alternatives="g_signal_connect_data" reason="Obsolete"/>
+    <arg nr="1"/>
+    <arg nr="2" direction="in"/>
+    <arg nr="3"/>
+    <arg nr="4"/>
+    <arg nr="5"/>
+    <arg nr="6"/>
+    <arg nr="7" direction="in"/>
+    <arg nr="8" direction="in"/>
   </function>
+  <!-- void gtk_signal_connect_object_while_alive (GtkObject *object,
+                                                   const gchar *name,
+                                                   GCallback func,
+                                                   GtkObject *alive_object); -->
   <function name="gtk_signal_connect_object_while_alive">
     <leak-ignore/>
     <noreturn>false</noreturn>
+    <returnValue type="void"/>
+    <warn severity="style" reason="Obsolete">gtk_signal_connect_object_while_alive is deprecated and should not be used in newly-written code. Use g_signal_connect_object() instead, passing G_CONNECT_SWAPPED as connect_flags.</warn>
+    <arg nr="1"/>
+    <arg nr="2" direction="in"/>
+    <arg nr="3"/>
+    <arg nr="4"/>
   </function>
   <function name="gtk_signal_connect_while_alive">
     <leak-ignore/>
     <noreturn>false</noreturn>
+    <warn severity="style" alternatives="g_signal_connect_object" reason="Obsolete"/>
   </function>
+  <!-- void gtk_signal_emit (GtkObject *object,
+                             guint signal_id,
+                             ...); -->
   <function name="gtk_signal_emit">
     <leak-ignore/>
     <noreturn>false</noreturn>
+    <returnValue type="void"/>
+    <warn severity="style" alternatives="g_signal_emit" reason="Obsolete"/>
+    <arg nr="1"/>
+    <arg nr="2" direction="in"/>
+    <arg nr="variadic"/>
   </function>
   <function name="gtk_signal_emit_by_name">
     <leak-ignore/>