The commit 16e673c2f6a0 ("cr-check: Inspect errno on syscall
failures") reverts the way the returned the error returned by kcmp is
checked. As a consequence 'criu check' is always failing with the
following message:

Error (cr-check.c:165): System call kcmp is not supported: No such process

This patch ensure is reported only if syscall(SYS_kcmp) returns
ENOSYS.

Fixes: 16e673c2f6a0 ("cr-check: Inspect errno on syscall failures")
Looks-good-to: Filipe Brandenburger <filbranden@google.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>