!122 set openGauss thread name and add getting function of t_thrd and u_sess

Merge pull request !122 from chenxiaobin/master

src/gausskernel/process/threadpool/knl_session.cpp

@@ -1140,3 +1140,8 @@ knl_session_context* create_session_context(MemoryContext parent, uint64 id)
     MemoryContextSwitchTo(old_cxt);
     return sess;
 }
+
+__attribute__ ((__used__)) knl_session_context *get_current_session()
+{
+    return u_sess;
+}