patch 8.1.2389: using old C style comments

Problem:    Using old C style comments.
Solution:   Use // comments where appropriate.
diff --git a/src/xdiff/xutils.h b/src/xdiff/xutils.h
index fba7bae..0bebd93 100644
--- a/src/xdiff/xutils.h
+++ b/src/xdiff/xutils.h
@@ -44,4 +44,4 @@
 
 
 
-#endif /* #if !defined(XUTILS_H) */
+#endif // #if !defined(XUTILS_H)