ZOOKEEPER-4810: Fix buf data race at format_endpoint_info()

format_endpoint_info() is widely called in the IO thread. And the
some ZOOAPIs will call this method too: zoo_cycle_next_server()
and zoo_get_current_server(). These APIs return the same static buffer
read/write by IO thread causes data race.

Author: fanyang89

zookeeper-client/zookeeper-client-c/src/zookeeper.c

@@ -5111,11 +5111,11 @@ int zoo_add_auth(zhandle_t *zh,const char* scheme,const char* cert,
 
 static const char* format_endpoint_info(const struct sockaddr_storage* ep)
 {
-    static char buf[134] = { 0 };
+    static __thread char buf[134] = { 0 };
     char addrstr[INET6_ADDRSTRLEN] = { 0 };
     const char *fmtstring;
     void *inaddr;
-    char is_inet6 = 0;  // poor man's boolean
+    char is_inet6 = 0; // poor man's boolean
 #ifdef _WIN32
     char * addrstring;
 #endif