bug#32246: 27.0.50; files-tests failure on Cygwin

[Eli Zaretskii]

> From: Ken Brown <kbrown@cornell.edu>
> Date: Thu, 26 Jul 2018 10:54:38 -0400
> Cc: 32246@debbugs.gnu.org
> 
> I think the doc is ambiguous on that.  The first sentence of the doc in 
> the elisp manual says, "Sometimes file names or their parts need to be 
> compared as strings, in which case it’s important to know whether the 
> underlying filesystem is case-insensitive."  This certainly suggests 
> that the file should exist, but there's no indication of what the 
> function returns for a non-existent file.  And the code doesn't attempt 
> to detect this case.
> 
> I don't know what the right solution is.

The usual solution is to pass the root of the volume to pathconf.