HPUX: Disable positional I/O

HPUX: Disable positional I/O

Some versions of HP-UX have the pread() and pwrite() functions, but
they behave in odd ways; most notably, ignoring the offset argument
when _FILE_OFFSET_BITS is defined to 64.

This is noted in recent gnulib documentation
<http://git.savannah.gnu.org/cgit/gnulib.git/tree/doc/posix-functions/pwrite.texi>,
and slightly less clear references to pread() being broken can be
found on the development mailing list for git itself.

It is not completely clear what specific HP-UX versions are affected
by this. An autoconf run-time test may also be insufficient, because
the same binaries should be usable on machines with broken and
non-broken pread() implementations. So, to be safe, disable positional
I/O on HP-UX unconditionally.

Reviewed-on: http://gerrit.openafs.org/3949
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 11b2c6d6fe4dbbf5a54ae1e08e979c35ab6b7fa0)

Change-Id: Iaa27ae965482aafd0f981e70ce33df438af650e9
Reviewed-on: http://gerrit.openafs.org/3964
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>