patch 8.0.1583: using C99 comment

Problem:    Using C99 comment.
Solution:   Use old style comment. (Kazunobu Kuriyama)
diff --git a/src/quickfix.c b/src/quickfix.c
index 7ee386d..e8fe59b 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -4099,7 +4099,7 @@
     win_T	*wp = NULL;
     qf_info_T	*qi = &ql_info;
     char_u	*au_name = NULL;
-    int		save_qfid = 0;  // init for gcc
+    int		save_qfid = 0;  /* init for gcc */
     int		res;
 
     switch (eap->cmdidx)