I managed to forgot that kernel erases R8...R11 regitster
prior returning to userspace from `int 0x80`:
https://lkml.org/lkml/2009/10/1/164

That was the reason for hang on gcc v6.1 on Jenkins/elsewhere:
https://ci.openvz.org/job/CRIU/job/CRIU-x86_64/branch/criu-dev/

Tested on gcc v6.1 locally, on Travis-CI:
https://travis-ci.org/0x7f454c46/criu/builds/183976899

travis-ci: success for pie: fix clobber registers for int 0x80 (rev2)
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Tested-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>