bug#12911: 24.3.50; let users decide where (& perhaps whether) `emacs_backtrace.txt' files are written

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: drew.adams@oracle.com,  12911@debbugs.gnu.org
> Date: Sun, 18 Nov 2012 23:07:25 -0500
> 
> >> No need to change anything on platforms where stderr works.
> > stderr works on Windows as well.  See the code I wrote.
> 
> If stderr works, then why do we need emacs_backtrace.txt?

For when the stuff written to stderr ends up in the Great Void, or
scrolls off the screen, or whatever.