You can just roll it yourself in the application logic and store as a raw binary column.

This all assuming you don't need to make queries along the axis of "give me every user with role X".

Yes and no: there is no bitmap SQL type, but at least MSSQL packs multiple BIT-columns on the same table into the same word/byte and then uses bit tests for filtering. I suspect Oracle and Postgresql can do the same, but I don't know for sure.