Fix for -fno-common

Index: tests/bgp_mpath_test.c
--- tests/bgp_mpath_test.c.orig
+++ tests/bgp_mpath_test.c
@@ -73,7 +73,7 @@ struct testcase_t__ {
 
 /* need these to link in libbgp */
 struct thread_master *master = NULL;
-struct zclient *zclient;
+extern struct zclient *zclient;
 struct zebra_privs_t bgpd_privs =
 {
   .user = NULL,