bug#12450: Remove configure's --without-sync-input option.

[Eli Zaretskii]

> Date: Sun, 16 Sep 2012 02:52:35 -0700
> From: Daniel Colascione <dancol@dancol.org>
> CC: Eli Zaretskii <eliz@gnu.org>, lekktu@gmail.com, rms@gnu.org, 
>  12450@debbugs.gnu.org
> 
> > OK, but at this point we don't know of any real problems
> > that we'd have by assuming SYNC_INPUT on MS-Windows.
> > SYNC_INPUT is a much simpler model than non-SYNC_INPUT,
> > so this is not surprising.
> 
> The cygw32 port uses SYNC_INPUT on Windows. I've been using it for
> almost a year in one form or another, and I haven't noticed any
> problems.

That's good to know, thanks.

> There might be a few lurking bugs, however: one thing that stands
> out is that w32term.c, unlike xterm.c, sets interrupt_input_pending,
> but doesn't set pending_signals.

Please tell the details about this.