syscalls/ipc/Makefile.inc: changed LIB to LIBIPC

Both lib.mk and testcases/kernel/syscalls/ipc/Makefile.inc set
LIB. It confuses make when both failes are included into a leaf Makefile.

Renamed LIB to LIBIPC in Makefile.inc.

The idea is by Cyril Hrubis <chrubis@suse.cz>

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
msgctl{08, 09, 10, 11}: cleanup

 * Moved common functions, definitions to libmsgctl.h, libmsgctl.c.
 * Changed tst_* in the children with printf + exit (or return).
 * Some cleanup.

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>