In Drupal 6 there was a module called Admin Role which allows you to make a superadmin role (same rights as superuser). This function is now in core (as of Drupal 7). So if you install Drupal 7, you get three roles by default: anonymous, authenticated, administrator.

However, when upgrading a site from D6 to D7, this new admin role is missing. How do I add this role or convert an existing custom role to be the admin role?