patch 9.0.0039: not all systems have GDK_KEY_dead_circumflex

Problem:    Not all systems have GDK_KEY_dead_circumflex. (Hisashi T Fujinaka)
Solution:   Add an #ifdef.

src/gui_gtk_x11.c

@@ -1246,6 +1246,7 @@ key_press_event(GtkWidget *widget UNUSED,
 	}
     }
 
+#ifdef GDK_KEY_dead_circumflex
     // Belgian Ctrl+[ workaround
     if (len == 0 && key_sym == GDK_KEY_dead_circumflex)
     {
@@ -1259,6 +1260,7 @@ key_press_event(GtkWidget *widget UNUSED,
 	// are confusing code downstream
 	return TRUE;
     }
+#endif
 
     if (len == 0)   // Unrecognized key
 	return TRUE;

src/version.c

@@ -735,6 +735,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    39,
 /**/
     38,
 /**/