bug#27585: segfault when evaluating a file containing only backticks

[Eli Zaretskii <eliz@gnu.org>]

> From: Steve Kemp <steve@steve.org.uk>
> Date: Wed, 05 Jul 2017 06:21:10 +0000
> 
> 
>   I've recently started fuzzing GNU Emacs, using the current git sources.
>  During the course of that work I stumbled upon this easily reproduced bug:
> 
>    deagol ~ $ perl -e 'print "`" x ( 1024 * 1024  * 12);' > t.el
>    deagol ~ $ /usr/bin/emacs --batch --script ./t.el
>    ..
>    Segmentation fault (core dumped)

Here it says:

  Re-entering top level after C stack overflow

and doesn't crash.

> > Most likely just a stack overflow.
> 
>   Agreed, but still I think a segfault is unexpected and could be
>  prevented.

See above: the machinery to try and prevent it exists, but it doesn't
always succeed.  And it really can't be 100% reliable.  So I'm unsure
what did you expect, and why.  Emacs generally gives you enough rope
to hang yourself; it's up to you not to be tempted to do so...

IOW: why would someone want to run such a silly "program"?