bug#30364: 26.0.91; thread crash on macos

[Aaron Jensen]

On Tue, Feb 27, 2018 at 9:30 AM, Paul Eggert <eggert@cs.ucla.edu> wrote:
> Nobody else commented, so I reformatted the patch a bit to be more in the
> Emacs style and installed the attached into master.

I forgot, but given that this is a show-stopper bug for a new
headline/experimental feature for Emacs 26, would it be worth applying
this to the emacs-26 branch as well?