Implement C11 annex K?

[Paul Eggert]

Joseph S. Myers wrote:
> * Some functions will need versions for _FILE_OFFSET_BITS=64 /
> _LARGEFILE64_SOURCE (e.g. tmpfile, fopen, freopen have such versions, so
> the _s variants of those functions should also have such versions).

Also, don't provide _FILE_OFFSET_BITS=32 versions.  Just support 
_FILE_OFFSET_BITS=64, and make it a compile- or link-time error to try 
to use Annex K with _FILE_OFFSET_BITS=32.

Regardless of whether one thinks Annex K is a good idea, its stated goal 
is more-reliable software.  Requiring it to support _FILE_OFFSET_BITS=32 
(which is deliberately *unreliable*) would be counterproductive make-work.