The SQL Server 2012 Upgrade Advisor has a poorly
undocumented prerequisite. If you go and try and install the Upgrade Advisor off of the SQL Server 2012 RTM media, you will get the following error:
The installer is looking for the SQL Server 2012 Transact-SQL ScriptDom component which is found as part of the SQL Server 2012 Feature Pack.
After you install the ScriptDom package, you will be able to install the Upgrade Advisor.