#include_next and removing of duplicate include dirs

[Benjamin Kosnik]

> A header named <std_cstddef.h> should be able to say simply
> #include <stddef.h>.  If that gets the wrong <stddef.h>, then we
> need to look at why libstdc++ needs to replace <stddef.h> in the
> first place.  You are only asking for endless nightmares creating
> headers with the same names as the libc headers.

Hey. Didn't I just answer this in my first reply to Jakub?

;)

This is a requirement of the C++ standard, see Annex D, "C" compatibility 
headers. 

Yes, I think it's stupid. Yes, it will make builds difficult. 
No, it's currently not implemented in the trunk sources.

That being said, if cpp could be architected to deal with this 
eventuality, it would be helpful.

thanks,
benjamin