patch 9.1.1531: confusing error with nested legacy function

Problem:  confusing error with nested legacy function
          (lacygoill)
Solution: clarify error message E1117 with :def or :func (Hirohito Higashi)

fixes: #17697
closes: #17702

Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index 1884220..fc0f8c5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -720,6 +720,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1531,
+/**/
     1530,
 /**/
     1529,