bug#43037: Eval error in the ‘c-lang-defvar’ or ‘c-lang-setvar’

[Eli Zaretskii]

> Date: Fri, 16 Oct 2020 06:14:17 -0400
> From: AC <achirvasub@gmail.com>
> Cc: 43037@debbugs.gnu.org
> 
> Literally seconds ago I compiled emacs-27, started it up with 'emacs -Q' and 
> then visited the blank file '~/new.js'. That error popped up.

I cannot reproduce this with stock Emacs 27.1, but I can reproduce
with the current emacs-27 branch.  The more detailed error message is
this:

  Eval error in the ‘c-lang-defvar’ or ‘c-lang-setvar’ for 
‘font-lock-comment-end-skip’ (fallback source eval - js-mode compiled with CC 
Mode 5.34 but loaded with 5.34.1): (error "‘c-font-lock-comment-end-skip’ got 
no (prior) value in js-mode (might be a cyclic reference)")

Alan, can you take a look, please?