默認宏定義

https://blog.csdn.net/sealyao/article/details/6169568

https://gcc.gnu.org/onlinedocs/cpp/Predefined-Macros.html#Predefined-Macros

https://stackoverflow.com/questions/1666802/is-there-a-class-macro-in-c

https://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html