Putting 2fddfb7ce770f into emacs-26?

[Eric Abrahamsen <eric@ericabrahamsen.net>]

I know it's a bit late in the day, but would it be okay to cherry-pick
61313f058c7a899c2fbce055d21 from master to emacs-26?

It's related to how EIEIO objects are written to file. Previously, the
written representation included a string label, which was later
obsoleted. Current emacs-26 code *assumes* the presence of a string
label: it discards it, but will fail without it.

The change in 61313f058c7a899c2fbce055d21 checks for the label and
conditionally ignores it, making the code more resilient when reading
objects written by a wider range of Emacs versions. A bit of
future-proofing.

Is that acceptable for emacs-26?

Thanks,
Eric