Fix implicit function declarations as they are not supported by clang16 with standard settings.

Bug: https://bugs.gentoo.org/874717

Signed-off-by: Pascal Jäger <pascal.jaeger@leimstift.de>

--- a/callbacks.c
+++ b/callbacks.c
@@ -33,6 +33,12 @@ gpointer create_progressbar_window (ChData *data);
 gboolean update_progress(gpointer data);
 gpointer async_lengthy_func(gpointer data);

+extern void scale_box_sensitive (ChData *data, gboolean sensitive);
+extern gshort move_earth_true (ChData *data);
+extern void get_and_set_options (ChData *data);
+extern gshort get_map_position (ChData *data);
+extern gboolean is_peters (ChData *data);
+extern void button_sensitive (ChData *data, gboolean sensitive);
 /***************************************
        Window Callbacks
 ***************************************/
--- a/sunlight.c
+++ b/sunlight.c
@@ -19,6 +19,8 @@

 #include "support.h"

+extern void change_wallpaper (ChData *data);
+
 void initialize_variables (ChData *data){
        data->var.gi_rd1 = 1;
        data->var.gi_rd2 = 1;