For this to work properly, we first need the test infrastructure to have support
for the `--output-directory` flag (see base CL)
Change-Id: I75f788d19ad3b4e9523830250c4a1c9de8418cda
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/104400
Reviewed-by: Johnni Winther <johnniwinther@google.com>