GCC headers and DJGPP port

[DJ Delorie]

> > It doesn't.  It shouldn't have to.  ANSI says that stdio.h provides
> > NULL.  
>
> so it is not all that clear that it is provided by stdio.h
> exclusively.

I didn't say exclusively.  I said stdio.h provides it.  Headers that
expect stdio.h to *relinquish* its provision of NULL are broken.  The
other djgpp headers that also provide NULL cooperate so that none of
them have to relinquish their provisions to the others.

> Please tell me how you implement the above requirement without testing
> whether NULL has been defined?

They all define it to exactly the same thing: 0