bug#53739: 28.0.91; "C-x d" fails when "emacs -Q" starts on NetBSD with plan9/bin on head of PATH

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: Eli Zaretskii <eliz@gnu.org>,  53739@debbugs.gnu.org
> Date: Fri, 04 Feb 2022 12:50:39 +0800
> 
> Van Ly <van.ly@sdf.org> writes:
> 
> > % /usr/local/plan9/bin/ls -l
> > d-rwxr-xr-x M 0 van staff 0 Feb  1 02:37 Configurations
> > d-rwxr-xr-x M 0 van staff 0 Feb  3 21:08 Examples
> > d-rwxr-xr-x M 0 van staff 0 Jan 25 20:38 Projects
> 
> That should probably work fine, so I have no idea what the problem might
> be.

The problem, as I explained up-thread, seems to be that 'ls' returns a
non-zero exit status, which insert-directory takes as a sign that the
directory listing didn't work.

So: what does "ls -l" return as exit status when using the plan9
variant of 'ls'?