Align ECM and Qt setup with Frameworks conventions
Summary:
This completes the previous commit which provided the hotfix for the ECM
version lookup issue breaking the build.
Reviewers: cgiboudeaux
Reviewed By: cgiboudeaux
Subscribers: cgiboudeaux, kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D26011