ECMQueryQt: Add fallbacks
Some applications look for ECM and need to know Qt paths but don't need to link to anything. That's the case for icons or wallpapers.
For these cases, ECMQueryQt will first try to find qmake or qtpaths before looking for Qt CMake config files.
Also handle cases where project() sets 'LANGUAGE' to 'NONE'. The CXX language needs to be enabled for find_package to look for Qt into library dirs.