Fix two warnings about possibly missing printf format attributes

app/widgets/gimptextbuffer-serialize.c

@@ -277,6 +277,13 @@ typedef struct
   GSList *tags;
 } TextSpan;
 
+static void set_error (GError              **err,
+                       GMarkupParseContext  *context,
+                       int                   error_domain,
+                       int                   error_code,
+                       const char           *format,
+                       ...) G_GNUC_PRINTF (5, 6);
+
 static void
 set_error (GError              **err,
            GMarkupParseContext  *context,

libgimpbase/gimpunit.c

@@ -345,6 +345,12 @@ gimp_unit_get_plural (GimpUnit unit)
   return _gimp_unit_vtable.unit_get_plural (unit);
 }
 
+static gint print (gchar       *buf,
+                   gint         len,
+                   gint         start,
+                   const gchar *fmt,
+                   ...) G_GNUC_PRINTF (4, 5);
+
 static gint
 print (gchar       *buf,
        gint         len,