https://www.gnu.org/software/make/manual/html_node/Automatic-Variables.html
https://blog.csdn.net/elfprincexu/article/details/51886620
https://www.cnblogs.com/wanqieddy/archive/2011/09/21/2184257.html
https://blog.csdn.net/gxlzyt123456/article/details/54965408
https://blog.csdn.net/qq_39498080/article/details/79237260
https://blog.csdn.net/qhexin/article/details/16951881
https://blog.csdn.net/xinyuan510214/article/details/50825633
https://stackoverflow.com/questions/5801754/gcc-directory-option-isystem