zdtm: rely on -D_GNU_SOURCE passed from Makefiles

After the commit
  02c763939c10 ("test/zdtm: unify common code")

CFLAGS with -D_GNU_SOURCE defined in the top Makefile
are being passed to tests Makefiles.
As _GNU_SOURCE is also defined by tests, that resulted in
zdtm tests build failures:

  make[2]: Entering directory `/home/criu/test/zdtm/lib'
   CC        test.o
  test.c:1:0: error: "_GNU_SOURCE" redefined [-Werror]
   #define _GNU_SOURCE
   ^
  <command-line>:0:0: note: this is the location of the previous definition
  cc1: all warnings being treated as errors
  make[2]: *** [test.o] Error 1

However, we didn't catch this in time by Travis-CI, as zdtm.py doesn't
do `make zdtm`, rather it does `make -C test/zdtm/{lib,static,transition}`.
By calling middle makefile this way, it doesn't have _GNU_SOURCE in
CFLAGS from top-Makefile.

I think the right thing to do here - is following CRIU's way:
rely on definition of _GNU_SOURCE by Makefiles.

This patch is almost fully generated with
  find test/zdtm/ -name '*.c' -type f					\
     -exec sed -i '/define _GNU_SOURCE/{n;/^$/d;}' '{}' \;		\
     -exec sed -i '/define _GNU_SOURCE/d' '{}' \;

With an exception for adding -D_GNU_SOURCE in tests Makefile.inc for
keeping the same behaviour for zdtm.py.
Also changed utsname.c to use utsname::domainname, rather private
utsname::__domainname, as now it's uncovered (from sys/utsname.h):
> struct utsname
>  {
...
> # ifdef __USE_GNU
>     char domainname[_UTSNAME_DOMAIN_LENGTH];
> # else
>     char __domainname[_UTSNAME_DOMAIN_LENGTH];
> # endif
Reported-by: Adrian Reber <areber@redhat.com>
Cc: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

test/zdtm/Makefile.inc

@@ -23,6 +23,7 @@ SRCARCH ?= $(ARCH)
 CC	:= gcc
 CFLAGS	+= -g -O2 -Wall -Werror -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=0
 CFLAGS	+= $(USERCFLAGS)
+CFLAGS	+= -D_GNU_SOURCE
 CPPFLAGS += -iquote $(LIBDIR)/arch/$(SRCARCH)/include
 
 ifeq ($(strip $(V)),)

test/zdtm/lib/fs.c

-#define _GNU_SOURCE
-
 #include <stdlib.h>
 #include <stdio.h>
 #include <stdarg.h>

test/zdtm/lib/lock.c

-#define _GNU_SOURCE
-
 #include <stdlib.h>
 #include <stdio.h>
 #include <stdarg.h>

test/zdtm/lib/ns.c

-#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>

test/zdtm/lib/test.c

-#define _GNU_SOURCE
 #include <stdio.h>
 #include <errno.h>
 #include <unistd.h>

test/zdtm/static/autofs.c

-#define _GNU_SOURCE
-
 #include <unistd.h>
 #include <stdio.h>
 #include <stdlib.h>

test/zdtm/static/caps00.c

-#define _GNU_SOURCE
 #include <errno.h>
 #include <unistd.h>
 #include <sys/types.h>

test/zdtm/static/cgroup_stray.c

-#define _GNU_SOURCE
 #include <unistd.h>
 #include <stdbool.h>
 #include <stdlib.h>

test/zdtm/static/cgroupns.c

-#define _GNU_SOURCE
 #include <unistd.h>
 #include <stdbool.h>
 #include <stdlib.h>

test/zdtm/static/clone_fs.c

-#define _GNU_SOURCE
 #include <stdlib.h>
 #include <syscall.h>
 #include <pthread.h>

test/zdtm/static/console.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>

test/zdtm/static/del_standalone_un.c

-#define _GNU_SOURCE
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>

test/zdtm/static/deleted_unix_sock.c

-#define _GNU_SOURCE
 #include <errno.h>
 #include <unistd.h>
 #include <stdlib.h>

test/zdtm/static/different_creds.c

-#define _GNU_SOURCE
 #include <alloca.h>
 #include <unistd.h>
 #include <stdbool.h>

test/zdtm/static/eventfs00.c

-#define _GNU_SOURCE         /* See feature_test_macros(7) */
 #include <unistd.h>
 
 #include <errno.h>

test/zdtm/static/fanotify00.c

-#define _GNU_SOURCE         /* See feature_test_macros(7) */
 #include <unistd.h>
 #include <limits.h>
 

test/zdtm/static/fdt_shared.c

-#define _GNU_SOURCE             /* See feature_test_macros(7) */
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>

test/zdtm/static/fifo-rowo-pair.c

-#define _GNU_SOURCE
 #include <unistd.h>
 
 #include <errno.h>

test/zdtm/static/file_fown.c

-#define _GNU_SOURCE         /* See feature_test_macros(7) */
 #include <unistd.h>
 
 #include <errno.h>

test/zdtm/static/file_locks00.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>

test/zdtm/static/file_locks01.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <fcntl.h>

test/zdtm/static/file_locks02.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <fcntl.h>

test/zdtm/static/file_locks03.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <fcntl.h>

test/zdtm/static/file_locks04.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <fcntl.h>

test/zdtm/static/file_locks05.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <fcntl.h>

test/zdtm/static/file_locks06.c

-#define _GNU_SOURCE
-
 #include <sys/file.h>
 #include <unistd.h>
 #include <fcntl.h>

test/zdtm/static/file_locks07.c

-#define _GNU_SOURCE
-
 #include <sys/file.h>
 #include <unistd.h>
 #include <fcntl.h>

test/zdtm/static/file_locks08.c

-#define _GNU_SOURCE
-
 #include <sys/wait.h>
 #include <sys/file.h>
 #include <unistd.h>

test/zdtm/static/groups.c

-#define _GNU_SOURCE
 #include <unistd.h>
 #include <errno.h>
 #include <stdlib.h>

test/zdtm/static/helper_zombie_child.c

-#define _GNU_SOURCE
 #include <unistd.h>
 #include <stdlib.h>
 #include <stdbool.h>

test/zdtm/static/inotify00.c

-#define _GNU_SOURCE         /* See feature_test_macros(7) */
 #include <unistd.h>
 #include <limits.h>
 

test/zdtm/static/inotify02.c

-#define _GNU_SOURCE
-
 #include <unistd.h>
 #include <limits.h>
 

test/zdtm/static/inotify_irmap.c

-#define _GNU_SOURCE         /* See feature_test_macros(7) */
 #include <unistd.h>
 #include <limits.h>
 

test/zdtm/static/maps01.c

-#define _GNU_SOURCE
 #include <errno.h>
 #include <fcntl.h>
 #include <unistd.h>

test/zdtm/static/mnt_ext_auto.c

-#define _GNU_SOURCE
 #include <sched.h>
 #include <sys/mount.h>
 #include <unistd.h>

test/zdtm/static/mnt_ext_master.c

-#define _GNU_SOURCE
 #include <sched.h>
 
 #include <sys/mount.h>

test/zdtm/static/mnt_tracefs.c

-#define _GNU_SOURCE
 #include <sched.h>
 #include <sys/mount.h>
 #include <unistd.h>

test/zdtm/static/mntns_deleted.c

-#define _GNU_SOURCE
-
 #include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>

test/zdtm/static/mntns_ghost.c

-#define _GNU_SOURCE
 #include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>

test/zdtm/static/mntns_link_remap.c

-#define _GNU_SOURCE
 #include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>

test/zdtm/static/mntns_open.c

-#define _GNU_SOURCE
 #include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>

test/zdtm/static/mntns_overmount.c

-#define _GNU_SOURCE
 #include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>

test/zdtm/static/mntns_remap.c

-#define _GNU_SOURCE
 #include <sched.h>
 #include <stdbool.h>
 #include <string.h>

test/zdtm/static/mntns_ro_root.c

-#define _GNU_SOURCE
 #include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>

test/zdtm/static/mntns_root_bind.c

-#define _GNU_SOURCE
 #include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>

test/zdtm/static/mntns_shared_bind.c

-#define _GNU_SOURCE
 #include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>

test/zdtm/static/mntns_shared_bind03.c

-#define _GNU_SOURCE
 #include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>

test/zdtm/static/mntns_shared_vs_private.c

-#define _GNU_SOURCE
 #include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>

test/zdtm/static/mountpoints.c

-#define _GNU_SOURCE
 #include <stdbool.h>
 #include <string.h>
 #include <fcntl.h>

test/zdtm/static/msgque.c

-#define _GNU_SOURCE
 #include <sched.h>
 
 #include <stdio.h>

test/zdtm/static/pid00.c

-#define _GNU_SOURCE
 #include <errno.h>
 #include <unistd.h>
 #include <sys/types.h>

test/zdtm/static/proc-self.c

-#define _GNU_SOURCE         /* See feature_test_macros(7) */
 #include <unistd.h>
 
 #include <errno.h>

test/zdtm/static/remap_dead_pid.c

-#define _GNU_SOURCE
 #include <string.h>
 #include <fcntl.h>
 #include <unistd.h>

test/zdtm/static/sem.c

-#define _GNU_SOURCE
 #include <sched.h>
 
 #include <stdio.h>

test/zdtm/static/session00.c

-#define _GNU_SOURCE
 #include <unistd.h>
 #include <stdlib.h>
 #include <sys/wait.h>

test/zdtm/static/session01.c

-#define _GNU_SOURCE
 #include <unistd.h>
 #include <stdlib.h>
 #include <string.h>

test/zdtm/static/session02.c

-#define _GNU_SOURCE
 #include <sys/mman.h>
 #include <sched.h>
 #include <unistd.h>

test/zdtm/static/session03.c

-#define _GNU_SOURCE
 #include <sys/mman.h>
 #include <sched.h>
 #include <unistd.h>

test/zdtm/static/shm-mp.c

-#define _GNU_SOURCE
 #include <unistd.h>
 #include <sys/mman.h>
 #include <sys/types.h>

test/zdtm/static/shm.c

-#define _GNU_SOURCE
 #include <sched.h>
 
 #include <stdio.h>

test/zdtm/static/sigaltstack.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <signal.h>

test/zdtm/static/signalfd00.c

-#define _GNU_SOURCE         /* See feature_test_macros(7) */
 #include <unistd.h>
 
 #include <errno.h>

test/zdtm/static/sigpending.c

-#define _GNU_SOURCE
 #include <signal.h>
 #include <stdlib.h>
 #include <unistd.h>

test/zdtm/static/sk-unix-rel.c

 
-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>

test/zdtm/static/sock_peercred.c

-#define _GNU_SOURCE
 #include <sched.h>
 #include <sys/socket.h>
 #include <sys/types.h>

test/zdtm/static/socket-ext.c

 
-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>

test/zdtm/static/socket-tcp.c

-#ifndef _GNU_SOURCE
-#define _GNU_SOURCE
-#endif
 #include "zdtmtst.h"
 
 #ifdef ZDTM_IPV6

test/zdtm/static/socket_dgram_data.c

-#define _GNU_SOURCE
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>

test/zdtm/static/socket_queues.c

 
-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>

test/zdtm/static/socket_snd_addr.c

-#define _GNU_SOURCE
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>

test/zdtm/static/sockets00.c

 
-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>

test/zdtm/static/sockets01.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>

test/zdtm/static/sockets02.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>

test/zdtm/static/sockets03.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>

test/zdtm/static/sockets_dgram.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>

test/zdtm/static/sockets_spair.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>

test/zdtm/static/tempfs_subns.c

-#define _GNU_SOURCE         /* See feature_test_macros(7) */
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/wait.h>

test/zdtm/static/utsname.c

@@ -36,7 +36,7 @@ int main(int argc, char **argv)
 		fail("Nodename doesn't match");
 		return 1;
 	}
-	if (strcmp(ZDTM_DOMAIN, after.__domainname)) {
+	if (strcmp(ZDTM_DOMAIN, after.domainname)) {
 		fail("Domainname doesn't match");
 		return 1;
 	}

test/zdtm/static/vt.c

-#define _GNU_SOURCE
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>

test/zdtm/static/xids00.c

-#define _GNU_SOURCE
 #include <unistd.h>
 #include <errno.h>
 #include <stdlib.h>

test/zdtm/transition/ipc.c

-#define _GNU_SOURCE
 #include <sched.h>
 
 #include <stdio.h>

test/zdtm/transition/maps008.c

-#define _GNU_SOURCE
 #include <stdlib.h>
 #include <stdbool.h>
 #include <string.h>

test/zdtm/transition/shmem.c

-#define _GNU_SOURCE
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>