LSB include headers lack support for large files

There is no support for _FILE_OFFSET_BITS=64 (or _LARGEFILE_SOURCE), i.e. the
"implicit LFS" support:
http://people.redhat.com/berrange/notes/largefile.html

The LSB ABI does support the explicit LFS interface, so it would be a matter of
updating the headers to support it as well.
The headers do support _LARGEFILE64_SOURCE, so thats a start, but according to
feature_test_macros(7) that is only a transitional macro and
_FILE_OFFSET_BITS=64 should be used instead.

Attached testcase fails on 32-bit x86 when built with the LSB SDK, but works
fine when built with system compiler:
$ ./test.sh
[...]
checking for _FILE_OFFSET_BITS value needed for large files... unknown
[...]

=== Testing system build ===
file8G size: 8589934592
=== Testing LSB build ===
file8G: Value too large for defined data type

There are a few choices for me here:
 * do not distribute 32-bit binary packages built with LSB, just require people
to build from source if they want to run the application on 32-bit
 * switch application to open64/stat64/etc. => not portable, not worth the
complications
 * fix the LSB headers so they do the renaming as with _FILE_OFFSET_BITS=64 and
system headers
 * just use system headers always, and rely only on the link time checks of LSB
(bit risky)