Fix -fno-common build error. Taken from
https://svnweb.freebsd.org/ports?view=revision&revision=549579

Index: mdnsd/mdns.c
--- mdnsd/mdns.c.orig
+++ mdnsd/mdns.c
@@ -45,6 +45,9 @@ extern struct mdnsd_conf	*conf;
 struct question_tree		 question_tree;
 struct cache_tree		 cache_tree;
 
+pg_q pg_queue;
+pge_q pge_queue;
+
 /*
  * RR cache
  */