To reproduce:

* Install fresh Fedora 34 VM
* Compile Bitcoin Core and run `./test/functional/p2p_dns_seeds.py`
{
    struct sigaction action = {};
    sigset_t mask;
    sigemptyset(&mask);
    sigaddset(&mask, SIGSYS);
    action.sa_sigaction = &SyscallSandboxDebugSignalHandler;
    action.sa_flags = SA_SIGINFO;
    if (sigaction(SIGSYS, &action, nullptr) < 0) {
        return false;
    }
    if (sigprocmask(SIG_UNBLOCK, &mask, nullptr)) {
        return false;
    }
    return true;
}
enum class SyscallSandboxAction {
    KILL_PROCESS,
    INVOKE_SIGNAL_HANDLER,
};
class SeccompPolicyBuilder