Syscalls do return negative value in case of an error.
But errno contains the error code itself.

Add uint32_t to sys_futex() definition.
sizeof(unsigned int) might be not 4 bytes.
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Adrian Reber <areber@redhat.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>