[CRIU] Bringin back former syscalls

[Cyrill Gorcunov]

Hi Laurent! You know in commit 8ceab588a5ce9151375bc3d2a6d6637d758764ab
we've been dropping off own __NR_ syscalls usage, which works quite
fine for modern distros where all syscalls we're using maps to SYS_
numbers from libc.

But it happen that we're running tests on old environments where
libc is not that fresh ones and we got the cases like

cr-check.c: In function ‘check_kcmp’:
cr-check.c:162:20: error: ‘SYS_kcmp’ undeclared (first use in this function)
cr-check.c:162:20: note: each undeclared identifier is reported only once for each function it appears in
cr-check.c: In function ‘check_prctl’:
cr-check.c:206:26: error: ‘PR_SET_MM_EXE_FILE’ undeclared (first use in this function)
cr-check.c:212:26: error: ‘PR_SET_MM_AUXV’ undeclared (first use in this function)
make[2]: *** [cr-check.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [built-in.o] Error 2
make: *** [criu] Error 2

(https://travis-ci.org/cyrillos/criu/jobs/110142700)

So I propose: either test all SYS_ entries on building stage via
feature-tests helper, either revert the commit.

Could you please take a look in this area?

(CC'ed more people, maybe there some easier solution?)

	Cyrill