> According to this message from 2014 [1] it was resolved, and the
> etc/PROBLEMS entry was removed.  But the entry is still there in current master.

That's due to a botched merge of etc/PROBLEMS in March 2015. Thanks for 
mentioning it. I installed the attached patch into master to fix it.

> I remember running into this a couple of weeks ago on a Debian
> jessie system, and the Emacs there is...  let's see...  25.1.1.  That's
> after 2014

Yes, the problem that I fixed in 2014 should not be present in Emacs 
25.1. Of course there could be some other problem with similar symptoms. 
I can't reproduce the symptoms, though. I tried running Emacs master on 
Fedora 27 with networking disabled (using Gnome's "Wired Connected > 
Turn Off" UI), and Emacs started up fine.