restore/x86: call int80 for compat sigaction restore

The kernel patch "x86/signal: add SA_{X32,IA32}_ABI sa_flags" makes
signal's ABI the same as sigaction's syscall ABI instead of per-thread's
TIF_IA32 flag.
So for delivering signals with compatible ABI, we need to call
sigaction through raw int80 exception.
This patch restores signals with int80: cr-restore part and PIE restorer's
part lay in sigaction_compat.c, which compiled for criu binary and for
restorer PIE.
The PIE's part is needed strictly for setting SIGCHLD handler, other
signal handlers are set in cr-restore (as it was before).

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