Does the attached patch work around the macOS bug? (I don't use macOS so 
can't easily test this.) The idea of this patch is to fix both the new 
bug with file-directory-p and the circa-2012 bug with 
file-accessible-directory-p.

The bug should probably be fixed in Gnulib so that Emacs proper is 
unaffected, but first I want to check whether this fix approach works.