[ob] fix mingw compilation

[Eli Zaretskii]

> From: Vladimir Prus <vladimir@codesourcery.com>
> Date: Tue, 30 Jan 2007 13:37:14 +0300
> 
> @@ -765,18 +768,20 @@ pipe_windows_close (struct serial *scb)
>  static int
>  pipe_windows_read (struct serial *scb, size_t count)
>  {
> -  HANDLE pipeline_out = (HANDLE) _get_osfhandle (scb->fd);
> +  HANDLE pipeline_out;

This one-line change is unnecessary; please put back the original
code, it's perfectly valid C, and shouldn't trigger any warnings or
errors from GCC.

The other changes are okay.

Thanks.