boot0.S empty #ifdef

[some body]

I am starting to learn how the kernel works and have started by going
through the boot loader and I've noticed that between lines 21-32 in
boot0.S there are some empty #ifdef statements. I was wondering a) where
are these paramaters defined and if they are defined, what difference does
it make since it looks like it doesn't change anything since they're empty?


#ifdef SIO
#endif

#ifdef CHECK_DRIVE
#endif

#ifdef ONLY_F_KEYS
#endif