Now that cosmocc is unpacked into a version-specific directory under
cosmocc/, it makes more sense to put the versions in /opt/cosmocc and
maintain a symlink to the currently active one.
- Check `$COSMOCC`, defaulting to `/opt/cosmocc`.
- Try to get the full path of the repo `make.com`. I'm not aware of
a way of getting the path that defines a zsh function, so the best
fallback available is `$PWD`.
`o/$mode/*` is passed through as-is. `o/*` other than `$mode` has
`$mode` inserted. `*` has `o/$mode/` prepended.
Really leveraging zsh default tab completion here; if you have built
things with `MODE=` you can leverage that for perfect tab completion
in other modes.
