properly show xfreerdp runtime dependency in cmake summary

Summary:
in absence of a proper finder we'll have a fake package find which we
force found depending on the find_program call.

this results in the runtime dep being reported as such in the cmake
feature summary

Test Plan:
rm -rf *; cmake ..

• executable found => reported found in summary
• executable !found => reported !found

Reviewers: KDE Applications, aacid

Reviewed By: KDE Applications, aacid

Subscribers: aacid, whiting

Differential Revision: https://phabricator.kde.org/D18151