说明：  makefile关系到了整个工程的编译规则。一个工程中的源文件不计数，其按类型、 功能、模块分别放在若干个目录中，makefile定义了一系列的规则来指定，哪些文件需 要先编译，哪些文件需要后编译，哪些文件需要重新编译，甚至于进行更复杂的功能 操作，因为makefile就像一个Shell脚本一样，其中也可以执行操作系统的命令。
(relations makefile to compile the rules of the whole project. A project source file does not count, its by type, function, module, respectively, on a number of directory, makefile definition of a series of rules to specify which files need to compile, after which files need to compile, which files need to re- compiler, and even more complex functions to operate, because makefile like a script, like Shell, which also can run operating system commands.)