Sigframe pointer should be fixed size.
Convert members of rt_sigframe_ia32 to fixed-size.
After this patch dumping of compatible tasks works.

Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>