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

[Eli Zaretskii]

> Date: Sun, 16 Sep 2012 09:30:27 -0700
> From: Paul Eggert <eggert@cs.ucla.edu>
> CC: Stefan Monnier <monnier@iro.umontreal.ca>, lekktu@gmail.com, 
>  12450@debbugs.gnu.org
> 
> On 09/16/2012 08:45 AM, Eli Zaretskii wrote:
> >> - The keyboard input or the X event causes a signal to be delivered.
> > Which signals are those, specifically?
> 
> SIGWINCH for window changes.
> 
> SIGIO, SIGINT and SIGQUIT for keyboard input, if interactive.
> But SIGIO is not used on platforms where it doesn't work.

Thanks, but what about X input events?

> And SIGQUIT is not caught on DOS_NT.

Because there's no SIGQUIT on Windows.  (And on DOS, keyboard
interrupts are disabled at startup, with the exception of Ctrl-BREAK.)