Indices in octave.pdf fail?

[Rik]

Is anyone else seeing this problem with the Octave manual on the
development branch?

If I go to the page for the Concept Index or Function Index or ... I find
just this bit of text

(Skipped sorted index file in obsolete format)

It was cumbersome, but I used hg bisect to track it down to this changeset

changeset:   27780:0dad96574d12
user:        Rik <address@hidden>
date:        Fri Dec 06 11:24:16 2019 -0800
summary:     maint: update gnulib ahead of 6.1 release.

Do we need to back this changeset out?  Should we update gnulib again in
case they have fixed whatever interaction there is with Texinfo?

--Rik