fixed to adapt gcc-5.4 & glibc-2.25

zhangmeng

2021-07-02 056f71f24cefaf88f2a93714c6678c03ed5f1e0e

 src/exported_symbols

@@ -7,6 +7,7 @@
   BHQueryTopicAddress;
   BHQueryProcs;
   BHSubscribeTopics;
   BHSubscribeNetTopics;
   BHStartWorker;
   BHHeartbeatEasy;
   BHHeartbeat;