bug#36649: 27.0.50; pure space and pdumper

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Date: Sun, 21 Jul 2019 19:56:42 +0200
> Cc: 36649@debbugs.gnu.org, Paul Eggert <eggert@cs.ucla.edu>
> 
>     Pip> That's strange. Looking at the crash backtrace again, it seems that
>     Pip> this is the initial garbage collection, when everything should be
>     Pip> pristine. I still think it dies while marking the obarray, upon
>     Pip> encountering a symbol which has somehow become corrupted...
> 
> OK. How do we go about detecting which symbol that is?

etc/DEBUG has some advice for debugging crashes inside GC.