includes exist for a reason. No reason to use badly written extern declarations
diff -ru gkrellsun-1.0.0.orig/src20/gkrellsun.c gkrellsun-1.0.0/src20/gkrellsun.c
--- a/src20/gkrellsun.c	2024-04-01 09:51:43.815461580 +0000
+++ b/src20/gkrellsun.c	2024-04-01 09:53:30.245006285 +0000
@@ -15,10 +15,9 @@
 #endif
 
 #include <math.h>
+#include <glib.h>
 
 /* splint */
-extern gchar* g_string_free (/*@only@*/ GString *, gboolean);
-extern void pango_font_description_free (/*@owned@*/PangoFontDescription *);
 
 #define PLUGIN_HEIGHT 54
 #define SUN_WIDTH 54