这是aws-iot-device-sdk-embedded-C示例。但是当我调用make命令时，出现如下错误：
~/environment/aws-iot-device-sdk-embedded-C/samples/linux/subscribe_publish_sample ((6c99912...)) $ make
make -C ../../../external_libs/mbedTLS
make[1]: Entering directory `/home/ec2-user/environment/aws-iot-device-sdk-embedded-C/external_libs/mbedTLS'
make[1]: *** No targets specified and no makefile found. Stop.
make[1]: Leaving directory `/home/ec2-user/environment/aws-iot-device-sdk-embedded-C/external_libs/mbedTLS'
make: *** [all] Error 2
如何生成和运行此示例？(我不是C开发人员，所以如果可能，请提供详细的答案(
原因是库缺少mbedTLS。
请前往：
/home/ec2-user/environment/aws-iot-device-sdk-embedded-C/external_libs/mbedTLS
并查看它的自述文件：
# Copy source code for mbedTLS into this directory
#
# You'll need to download mbedTLS from the official ARMmbed repository and
# place the files here. We recommend that you pick the latest version of 2.16
# LTS release in order to have up-to-date security fixes.