seccomp: Fix building issue on recent kernels

The seccomp_metadata may be already defined in
system ptrace.h header on recent kernels so
include it.

https://github.com/checkpoint-restore/criu/issues/486#event-1628406918Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/seccomp.c

@@ -2,6 +2,7 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
+#include <ptrace.h>
 
 #include "common/config.h"
 #include "imgset.h"