wasi preview1 + threads `Thread` type missing `Drop` that calls `pthread_detach`

[programmerjake]

there is no pthread_detach call (there is no impl Drop at all), so users that want to create a detached thread end up leaking the pthread_t handle.

compare to the Unix Thread:

rust/library/std/src/sys/unix/thread.rs

Lines 280 to 285 in 8e7fd55

	impl Drop for Thread {
	fn drop(&mut self) {
	let ret = unsafe { libc::pthread_detach(self.id) };
	debug_assert_eq!(ret, 0);
	}
	}

[programmerjake]

since you made the commit, cc @g0djan

[programmerjake]

closing since the fix was merged