说明：  嵌入式Makefile设计， 为gprs项目编写Makefile文件。要求写三个Makefile文件，分别是：（1）使用了自动变量和基本规则的makefile；（2）使用隐式规则实现的makefile；（3）使用模式规则实现的makefile。
(Embedded Makefile design for the GPRS project to write Makefile files. It is required to write three Makefile files, namely: (1) makefile with automatic variables and basic rules; (2) makefile implemented by implicit rules; (3) makefile implemented by pattern rules)