fix(tools/mg): Support applying args to mg run (empty-target) r/5329

With this, we can disambiguate the following `mg run` invocations:

```shell
$ mg run :foo    # run the virtual target, foo, with no args
$ mg run -- :foo # run the empty target and pass the arg, :foo, to it
```

Change-Id: Id6395b36a4d8ef3f325937e322e1c27b8630b556
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7408
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Reviewed-by: sterni <sternenseemann@systemli.org>

0 files changed, 0 insertions, 0 deletions