fixed build error for mqtt_multi_thread-example

[doc] relocate config.mdm9206.sim7000c to doc/

* IoT SDK v2.0.2 在simcom7000C平台使用如下命令序列压力测试：

    mqtt a {ProductKey} {DeviceName} {DeviceSecret}
    mqtt c 60000 0 2000
    mqtt s data
    mqtt t 172800 3000 data hello

> code

    case 't':
    {
        int loop = 0;
        int rc=0;
        iotx_mqtt_topic_info_t topic_msg;
        char topic_data[100]={0};
        if (NULL == pclient) {
            QCLI_Printf(qcli_iotkit_handle, "need constructed first\n");
            break;
        }
        if (Parameter_Count != 5)
            return QCLI_STATUS_USAGE_E;
        QCLI_Printf(qcli_iotkit_handle,
            "####IOT_MQTT_Yield times:%d,timeout:%d,topicName:%s,payload:%s\n",
            Parameter_List[1].Integer_Value,
            Parameter_List[2].Integer_Value,
            Parameter_List[3].String_Value,
            Parameter_List[4].String_Value);
        memset(&topic_msg, 0x0, sizeof(iotx_mqtt_topic_info_t));
        topic_msg.qos = IOTX_MQTT_QOS1;
        topic_msg.retain = 0;
        topic_msg.dup = 0;
        topic_msg.payload = (void *)Parameter_List[4].String_Value;
        topic_msg.payload_len = strlen(topic_msg.payload);
        sprintf(topic_data, "/%s/%s/%s", product_key, device_name, Parameter_List[3].String_Value);

        for (loop = 0; loop < Parameter_List[1].Integer_Value; ++loop) {
            rc = IOT_MQTT_Publish(pclient, topic_data, &topic_msg);
            QCLI_Printf(qcli_iotkit_handle, "IOT_MQTT_Publish rc:%d\n",rc);
            rc = IOT_MQTT_Yield(pclient,Parameter_List[2].Integer_Value);
            QCLI_Printf(qcli_iotkit_handle, "IOT_MQTT_Yield rc:%d\n",rc);
        }
    }
    break;

运行约9小时卡死，期间有34次掉线尝试重连，其中12次重连成功

* 初步分析:

    - 进行高频压测IOT_MQTT_Yield，发现程序阻塞在HAL_SSL_Write
    - socket丢失链路，HAL_SSL_Write无法及时发现链路断开

* 结论: V2.02版本, 暂不发布SIM7000C版本, 移入doc/目录仅作参考

Signed-off-by: Yang, Xiao <[email protected]>

[MAKE] remove unused static library file.

[MAKE] MQTT_DIRECT by default and skip ANSI_C for src/coap

Signed-off-by: Yang, Xiao <[email protected]>