tar: port --overwrite symlink test to GNU/Hurd

Problem reported by Pino Toscano in
<http://lists.gnu.org/archive/html/bug-tar/2012-01/msg00040.html>.
* gnulib.modules: Add fcntl-h, which defines
HAVE_WORKING_O_NOFOLLOW.
* src/extract.c (open_output_file): Use HAVE_WORKING_O_NOFOLLOW,
not O_NOFOLLOW, when testing whther O_NOFOLLOW works.

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gnulib.modules

@@ -12,6 +12,7 @@ dirname
 error
 exclude
 exitfail
+fcntl-h
 fdopendir
 fdutimensat
 fileblocks

src/extract.c

@@ -887,7 +887,8 @@ open_output_file (char const *file_name, int typeflag, mode_t mode,
   /* If O_NOFOLLOW is needed but does not work, check for a symlink
      separately.  There's a race condition, but that cannot be avoided
      on hosts lacking O_NOFOLLOW.  */
-  if (! O_NOFOLLOW && overwriting_old_files && ! dereference_option)
+  if (! HAVE_WORKING_O_NOFOLLOW
+      && overwriting_old_files && ! dereference_option)
     {
       struct stat st;
       if (fstatat (chdir_fd, file_name, &st, AT_SYMLINK_NOFOLLOW) == 0