bug#29712: 26.0.90; Three emacs-26 elisp tests are failing on darwin

[Eli Zaretskii]

> Date: Sat, 16 Dec 2017 15:07:32 +0000
> From: Alan Third <alan@idiocy.org>
> Cc: 29712@debbugs.gnu.org
> 
> > Does it help to bind file-name-coding-system to utf-8-hfs-unix in that
> > test?
> 
> Yes, the test passes.

Then I think this is the right fix.

Maybe we should do that by default on Darwin, as it makes little sense
to convert EOLs in file names?  Did the changeset in 83f0d60 on master
did that for Darwin as well?