fix a compilation warning

src/or/circuitbuild.h

@@ -61,8 +61,10 @@ const node_t *choose_good_entry_server(uint8_t purpose,
 
 #ifdef CIRCUITBUILD_PRIVATE
 STATIC circid_t get_unique_circ_id_by_chan(channel_t *chan);
+#if defined(ENABLE_TOR2WEB_MODE) || defined(TOR_UNIT_TESTS)
 STATIC const node_t *pick_tor2web_rendezvous_node(router_crn_flags_t flags,
                                                   const or_options_t *options);
+#endif
 
 #endif