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

[Eli Zaretskii]

> Date: Sun, 16 Sep 2012 01:23:28 -0700
> From: Paul Eggert <eggert@cs.ucla.edu>
> CC: rms@gnu.org, lekktu@gmail.com, 12450@debbugs.gnu.org
> 
> On 09/15/2012 11:10 PM, Eli Zaretskii wrote:
> > I still would like to have BLOCK_INPUT in xmalloc and friends,
> > conditioned on some global variable being non-zero.
> 
> There is no need for that, if we've checked our signal handlers to
> make sure that they invoke only async-signal-safe functions.

Nevertheless, please humor me.

> > That thread left the MS-Windows case indeterminate.
> 
> OK, but at this point we don't know of any real problems
> that we'd have by assuming SYNC_INPUT on MS-Windows.

All I meant to say is that the jury is still out on this issue.  That
we don't know any better now does not settle the issue in any way.  A
few minutes of my running with SYNC_INPUT aren't a convincing
evidence, either.  So please don't try to make this look as a
non-issue; only the future will tell.