compiler: add ASSIGN_TYPED and ASSIGN_MEMBER

Looks like it's the most appropriate place for those hooks.
Didn't know about those helpers - maybe I should have used
them in my code more widely instead of casts.

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