Tests are now executed in a test-specific temporary directory, so test
output on failure should be reproducible/reusable as-is without needing
to have TMPDIR defined (as it only exists by default under macOS).
Aside from the fact that the shared state could cause problems, tests
were randomly assuming it would be created where that wasn't the case.
In particular, `redirect.fish` and `basic.fish` were failing on only
macOS because `../test/temp` didn't exist yet - it would be created by
other tests later.
Glob ordering is used in a variety of places, including figuring out
conf.d and really needs to be stable.
Other ordering, like completions, is really just cosmetic and can
change if it makes for a nicer experience.
So we uncouple it by copying the wcsfilecmp from 3.0.2, which will
return the ordering to what it was in that release.
Fixes#6593
Solaris/OpenIndiana/Illumos `rm` checks that and errors out.
In these cases we don't actually need it to be a part of $PWD as
it's just for cleanup, so we `cd` out before.
See #5472
See 1ee57e9244Fixes#6555Fixes#6558
