bug#64516: [PATCH] docview: Only enable imenu when supported

[Eli Zaretskii]

> From: Tassilo Horn <tsdh@gnu.org>
> Cc: Eli Zaretskii <eliz@gnu.org>, 64516@debbugs.gnu.org, jao@gnu.org
> Date: Tue, 18 Jul 2023 21:14:35 +0200
> 
> Alright, I've amended your patch with my slight modifications.  Eli,
> feel free to "git am" it where you see fit.  It should apply both on
> master and on emacs-29.

Thanks to both of you.  I've now installed this on the master branch,
and I'm closing the bug.