虐待gcc

-bash-3.2$ cat 0.c
#if __INCLUDE_LEVEL__ < N
#include "0.c"
#include "0.c"
#endif

#if __INCLUDE_LEVEL__ == 0
int main()
{
}
#endif

-bash-3.2$ gcc -DN=20 0.c
-bash-3.2$ gcc -DN=30 0.c