message: Clarify FIXME.
diff: @@ -357,7 +357,12 @@ impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
  if self.threads[MAIN_THREAD].state == ThreadState::Terminated {
  // The main thread terminated; stop the program.
  if self.threads.iter().any(|thread| thread.state != ThreadState::Terminated) {
  - // FIXME: This check should be either configurable or just emit a warning.
  + // FIXME: This check should be either configurable or just emit
  + // a warning. For example, it seems normal for a program to
  + // terminate without waiting for its detached threads to
  + // terminate. However, this case is not trivial to support
  + // because we also probably do not want to consider the memory
  + // owned by these threads as leaked.
  throw_unsup_format!("the main thread terminated without waiting for other threads");
  }
  return Ok(SchedulingAction::Stop);
  