The test for DNS cache entries left locked is now only built if

AGGRESIVE_TEST is also defined, as an addition to MALLOCDEBUG. It doesn't
work for multi interface usage and should only be used with careful
consideration.

lib/hostip.c

@@ -191,7 +191,7 @@ hostcache_prune(curl_hash *hostcache, int cache_timeout, int now)
                                  hostcache_timestamp_remove);
 }
 
-#ifdef MALLOCDEBUG
+#if defined(MALLOCDEBUG) && defined(AGGRESIVE_TEST)
 /* Called from Curl_done() to check that there's no DNS cache entry with
    a non-zero counter left. */
 void Curl_scan_cache_used(void *user, void *ptr)

lib/url.c

@@ -2854,7 +2854,7 @@ CURLcode Curl_done(struct connectdata *conn)
   if(conn->connect_addr)
     Curl_resolv_unlock(conn->connect_addr); /* done with this */
 
-#ifdef MALLOCDEBUG
+#if defined(MALLOCDEBUG) && defined(AGGRESIVE_TEST)
   /* scan for DNS cache entries still marked as in use */
   Curl_hash_apply(data->hostcache,
                   NULL, Curl_scan_cache_used);