crtools binary is linked with the C library and could rely on all the
services this library is providing, including system calls.

Thus it doesn't need to be linked with the builtin system calls code
made for the parasite/restorer binaries.

This patch does:
 - remove the inclusion of syscall.h
 - replace all call to sys_<syscall>() by C library <syscall>()
 - replace unwrapped system calls by syscall(SYS_<syscall>,...)
 - fix the generated compiler's issues.

There should not be any functional changes. The only 'code' changes is
appearing in locks.h when futex is called through the C library, the
errno value is fetched from errno variable instead of the return
value.
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Reviewed-by: Christopher Covington <cov@codeaurora.org>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>