Make `seccomp` an optional feature

[slhmy]

For a more flexible use(EX. we only want to monitor the rusage of the program, this can be used in MacOS which doesn't include libseccomp), libseccomp may not be included.

Also considering making judger just being the runner | dispatcher of the judge in the throw away container, in this case seccomp will be nearly useless and user group and namespace will be more necessary.