Allow additional arguments to be passed to GHC
This allows us to run validation builds with -dcore-lint.
Due to a large amount of spam we do not allow new users to create repositories, they are "external" users. If you are a new user and want to create a repository, for example for forking GHC, open a new issue on ghc/ghc using the "get-verified" issue template
This allows us to run validation builds with -dcore-lint.