`Condvar::wait_timeout` not supported

[mkroening]

@stlankes, in hermit-os/kernel@6cfaee1 for #117 you introduced sys_block_current_task_with_timeout.

I had a look at using std::thread::park_timeout instead. It's implemented using std::sync::Condvar::wait_timeout which is currently not supported on hermit (rust-lang/rust/library/std/src/sys/hermit/condvar.rs).

Do you think, it would be worth the time to add support and go that route instead?

[mkroening]

Okay, wow. I confused park_timeout with sleep, which should be a drop-in-replacement for sys_block_current_task_with_timeout.

So we don't need this for a nicer #117, but since the work is done, we might as well add support for Condvar::wait_timeout.