Those are useful for the cmake internal classes, but need to be filtered
out when they are going to get displayed to the users.

Change-Id: I0bb62fa840fa8cb9e6f3b47300ba85a2b186bad0
Reviewed-by: Alexander Drozdov <adrozdoff@gmail.com>
Reviewed-by: Tim Jenssen <tim.jenssen@theqtcompany.com>
Reviewed-by: Niels Weber <niels.weber@theqtcompany.com>