[PATCH] Always check lockf64 return value

[H.J. Lu]

On x86-64, when GCC 14.2.1 is used to build:

commit f3c82fc1b41261f582f5f9fa12f74af9bcbc88f9
Author: Radko Krkos <krkos@mail.muni.cz>
Date:   Sat Jun 14 11:07:40 2025 +0200

    io: Mark lockf() __wur [BZ #32800]

    In commit 0476597b28 flock() was marked __wur in posix/unistd.h, but not
    in io/fcntl.h, the declarations must match.

    Reviewed-by: Florian Weimer <fweimer@redhat.com>

I got

programs/locarchive.c: In function ‘open_archive’:
programs/locarchive.c:641:18: error: ignoring return value of
‘lockf64’ declared with attribute ‘warn_unused_result’
[-Werror=unused-result]
  641 |           (void) lockf64 (fd, F_ULOCK, sizeof (struct locarhead));
      |                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
programs/locarchive.c:653:14: error: ignoring return value of
‘lockf64’ declared with attribute ‘warn_unused_result’
[-Werror=unused-result]
  653 |       (void) lockf64 (fd, F_ULOCK, sizeof (struct locarhead));
      |              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
programs/locarchive.c:660:14: error: ignoring return value of
‘lockf64’ declared with attribute ‘warn_unused_result’
[-Werror=unused-result]
  660 |       (void) lockf64 (fd, F_ULOCK, sizeof (struct locarhead));
      |              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
programs/locarchive.c:679:14: error: ignoring return value of
‘lockf64’ declared with attribute ‘warn_unused_result’
[-Werror=unused-result]
  679 |       (void) lockf64 (fd, F_ULOCK, sizeof (struct locarhead));
      |              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Update locarchive.c to always check lockf64 return value.  This fixes
BZ #33089.

-- 
H.J.
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