[ruby-core:87040] Re: cross-thread IO#close semantics

[Eric Wong <normalperson@yhbt.net>]

Likewise, IO.copy_stream also fails to detect cross-thread
IO#close because it does not use waiting_fd infrastructure
in rb_thread_io_blocking_region.

```
r, w = IO.pipe
th = Thread.new do
  begin
    IO.copy_stream(r, '/dev/null')
  rescue => e
    warn [ e.class, e.message ].inspect
  end
end
sleep 0.1
r.close
th.join
```

Should I change IO.copy_stream and IO.select to avoid
stuck threads in these cases?