cmd/cue: fix tests under different platforms
Normalize filenames under Windows.
Copy with the fact that `ls` returns different status codes in different platforms.
Change-Id: I689fc08c152fc84190444171fee70d2bbb258ba5
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/3480
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
authored by