The arch field is the same for x86_64 and x32, thus checking it
is not enough.
Simply using x32 system calls would allow a bypass. Thus,
we must check whether the system call number is in __X32_SYSCALL_BIT.
This is of course a lazy solution, we could also add the
same system call number + _X32_SYSCALL_BIT to our black/whitelists.
For now however, this however will do.