print output log warning (#14497)

test=develop

Author: chengduo

paddle/fluid/platform/init.cc

@@ -38,6 +38,7 @@ std::once_flag p2p_init_flag;
 
 void InitGflags(std::vector<std::string> argv) {
   std::call_once(gflags_init_flag, [&]() {
+    FLAGS_logtostderr = true;
     argv.insert(argv.begin(), "dummy");
     int argc = argv.size();
     char **arr = new char *[argv.size()];