I don't think this impacts anyone today, since there are currently no unsupported roles listed in axe-core. But I noticed the following bugs.

• The value is not set, even though it's used in the fail message
• dpub roles can not be listed as unsupported, because they are ignored by default in getRole
• a role attribute using a fallback roles will not recognise the unsupported role, even if it's the first (role="unsupported button")

We can easily solve this by replicating what we did in the deprecatedrole check.