Looks like a Qt version skew problem; http://doc.qt.io/qt-5/qjsonarray.html suggests that in the current Qt, the QJsonArray constructors take either zero or one arguments, and the code is trying to invoke this one introduced in Qt 5.4 http://doc.qt.io/qt-5/qjsonarray.html#QJsonArray-2, while your installation of Qt5 seems to only declare a two-argument constructor and the copy-constructor.
You probably already knew that, but I think it means the cure is probably to install Qt 5.4 (or the prerelease 5.5) from source.
Do you see other compile problems if you run make -k, or just that one?
After updating qt5base-dev using debian experimental, and adding -fPIC to the CXXFLAGS, it compiled nicely :)
edit: there seems to be a slight problem with text rendering tho(only lowercase 'a' and bullet points are drawn), see http://imgur.com/MiX1hvL More of a qt5 issue I think
You probably already knew that, but I think it means the cure is probably to install Qt 5.4 (or the prerelease 5.5) from source.
Do you see other compile problems if you run make -k, or just that one?