http://www.ruanyifeng.com/blog/2015/02/make.html Make 命令教程
1. https://gist.github.com/isaacs/62a2d1825d04437c6f08 Isaac Schlueter的《Makefile文件教程》
2. https://www.gnu.org/software/make/manual/make.html GNU make
3. https://learnxinyminutes.com/docs/make/ Learn X in Y minutes
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底部：
4. https://www.gnu.org/software/make/manual/ GNU Operating System
5. http://swcarpentry.github.io/make-novice/ Automation and Make
6. https://stackoverflow.com/questions/448910/what-is-the-difference-between-the-gnu-makefile-variable-assignments-a What is the difference between the GNU Makefile variable assignments =, ?=, := and +=?