libc/gcc源码级 理解
#define va_start(v,l) __builtin_va_start(v,l)
#define va_end(v) __builtin_va_end(v)
#define va_arg(v,l) __builtin_va_arg(v,l)
https://zhuanlan.zhihu.com/p/268091445
https://reticenceji.github.io/post/gcc-ke-bian-can-shu-de-shi-yong-he-yuan-li/
未完待续!!!