patch 8.1.0405: too many #ifdefs for GTK

Problem:    Too many #ifdefs for GTK.
Solution:   Define macros instead of using #ifdef. (Ken Takata, closes #3436)
diff --git a/src/version.c b/src/version.c
index ec76b99..bfebd24 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    405,
+/**/
     404,
 /**/
     403,