This happens because you build Slicer against Qt4 + VTK7.
I suggest you build against Qt5. Simply doing a clean build passing -DQt5_DIR:PATH=/path/to/lib/cmake/Qt5 should be sufficient.
That said, I will fix the error because code up to the next release (Slicer 4.10.0) that will be cut tonight or tomorrow will be the last one to support compiling against both Qt4/VTK7 and Qt5/VTK9.