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/xemit.h b/src/xdiff/xemit.h
index 1b9887e..3ce7e3d 100644
--- a/src/xdiff/xemit.h
+++ b/src/xdiff/xemit.h
@@ -33,4 +33,4 @@
 
 
 
-#endif /* #if !defined(XEMIT_H) */
+#endif // #if !defined(XEMIT_H)