宏实现alignof

c11的特性，用一个宏来巧妙实现

#define AlignOf(type_) (offsetof(struct { char c; type_ t; }, t))

http://wangcong.org/blog/archives/1924
http://wangcong.org/blog/archives/category/%E7%BC%96%E7%A8%8B

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3093.html
http://imcc.blogbus.com/logs/144093548.html