bug#11519: "Wrong type argument: characterp" building custom-deps while boostrapping

[Eli Zaretskii <eliz@gnu.org>]

> From: Juanma Barranquero <lekktu@gmail.com>
> Date: Sat, 19 May 2012 23:40:06 +0200
> Cc: 11519@debbugs.gnu.org
> 
> > Can you try finding out which file in lisp/language causes that, and
> > on which line?
> 
> Yes, but it is slow; it only happens on bootstraps.

If you started looking, I think you can stop.  It's a %$#@!
heisenbug.  If I add a single (message %s file) to
custom-make-dependencies, it displays ethio-util.el as the last file
name before the error.  But adding another message makes the problem
disappear, and the bootstrap runs flawlessly to completion.  Likewise,
running just "make custom-deps" with the emacs.exe built by the first
stage of the bootstrap doesn't produce any errors.

I will try a few more tricks; ideas for how to debug this, or where to
look, are welcome.

If you say that this started happening only lately, perhaps bisecting
might give some insights.

Thanks.