In Tor simulations we currently get some warnings about futex operations that we don't support yet. We return ENOSYS for these, and as far as we can tell, this is handled gracefully without adversely affecting the simulation.

We probably ought to implement these operations though to increase our assurance about correctness in Tor simulations, get rid of the warnings, and support other simulations where they might really be needed.

Previously I've run across that glibc semaphores use FUTEX_WAIT_BITSET and FUTEX_WAKE_BITSET, so we probably ought to implement those. There might be others that are generating warnings in the tor simulations, though.