The kernel does touch only relevant union member on x86_32.

travis-ci: success for zdtm/sigpending/32: check only 12 bytes of _si_fields
Cc: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>