问题：
gcc编译器似乎对宏编译指令不支持宏替换，比如：
#define PACK1 pack(1)
#pragma PACK1
回答：
gcc 不支持#pragma行上的宏替换，参见:
info gcc
5.25 Declaring Attributes of Functions
...
Some people object to the `__attribute__' feature, suggesting that
ISO C's `#pragma' should be used instead. At the time `__attribute__'
was designed, there were two reasons for not doing this.
1. It is impossible to generate `#pragma' commands from a macro.
2. There is no telling what the same `#pragma' might mean in another
compiler.
...
如此说来，使用#pragma在不同的编译器之间很难保证兼容性，
假如非要用的话，至少在gcc下是不能同时使用宏替换的。
