stat-time: silence -Wunused-parameter regression
Commit
2c5d5587 causes warnings on non-Sun systems when compiled
under -Wunused-parameter; we've previously tweaked code in commit
81eb8486 to avoid such warnings. Prefer an attribute rather than
a cast to void (the attribute is always okay to apply; gcc
interprets it as 'may be unused', not 'must not be used', precisely
to cater to #if chains where determining whether or not the
parameter is used gets hairy).
* lib/stat-time.h (get_stat_birthtime_ns, get_stat_birthtime):
Prefer attribute over cast-to-void.
(stat_time_normalize): Mark st as potentially unused.
Signed-off-by: Eric Blake <eblake@redhat.com>