Clean up glibc manual references to "GNU system" (bug 6911)

[Roland McGrath]

> It's fuzzy what is or is not a GNU system - after all, a system could use 
> glibc but not have other GNU software installed in userspace, for example.  
> I'd imagine that a GNU/kFreeBSD system could have bits of normal FreeBSD 
> userspace installed alongside the glibc-based userspace.

The closest practical definition floating in the world really is that a GNU
system is a general-purpose POSIX-like operating system with glibc as its
system C library.  But that's not really it either--ultimately it's a
decision for GNU Central, and not entirely a technical one.  (I don't think
we'd ever say that a system composed entirely of glibc and other free
libraries, GNU utilities, and a proprietary kernel, could be a GNU system,
for example.)

I can't think of instances where the libc manual discusses what other
utilities do--it's only the manual for the C library, after all.  So for
the purposes of this manual, when we say "GNU systems" we're talking about
the C library and the operating system components it relies on (kernel and
the like), not the entirety of what goes into the user experience.


Thanks,
Roland