patch 8.2.2337: configure test for GTK only says "no"

Problem:    Configure test for GTK only says "no". (Harm te Hennepe)
Solution:   Hint that a -def package is needed. (closes #5229)
diff --git a/src/version.c b/src/version.c
index d4b5dde..47a5bcc 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2337,
+/**/
     2336,
 /**/
     2335,