Force git clean to remove dirs with .git repos (#528)
Force git clean to remove dirs with .git repos (#528)

- Git clean -fxd will not remove directories
  that contain a Git repository (.git folder).
- Adding a second force will remove these folders
- Ref https://git-scm.com/docs/git-clean#git-clean---force

Signed-off-by: Adam Brousseau <5bbd7b5b6d6d4bf0bd621a96b144468d4f2a15aa@gmail.com>
AdoptOpenJDK/openjdk-build,karianna/openjdk-build,AdoptOpenJDK/openjdk-build,karianna/openjdk-build