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

[Eli Zaretskii]

> Date: Sun, 16 Sep 2012 01:34:52 -0700
> From: Paul Eggert <eggert@cs.ucla.edu>
> CC: rms@gnu.org, 12450@debbugs.gnu.org, lekktu@gmail.com
> 
> > we cannot be sure whether its non-invocation on
> > SYNC_INPUT platforms isn't a simple omission, because most Posix
> > platforms use neither gmalloc nor ralloc.c.
> 
> I'm not sure how you're counting, but many POSIXish systems use gmalloc.
> These include FreeBSD, NetBSD, OpenBSD, HP-UX, AIX, and IRIX.

Most people here use GNU/Linux, which doesn't.  I don't know what
Stefan used to test SYNC_INPUT.

> Of course it's possible that there are memory allocation glitches
> on such systems, glitches that we haven't caught in the four years we've
> been using SYNC_INPUT.  But any such glitches would be an independent
> bug, i.e., a bug that we should fix independently of whether we remove
> --without-sync-input.

I'm not talking about removing the option, I'm talking about what
should and shouldn't be done as part of that removal.  You suggest
removing some part whose significance we do not understand in full.
We can either dig into the related code and our memories and
understand those parts, or we can play it safe and not remove the
parts we don't understand.  Any third possibility would be acting
irresponsibly on our part.

> And the glitches can't be that serious, or we'd have noticed them
> before now.

See bug #12242, for a demonstration of how easy to notice such bugs.