Missing FindosgQt.cmake
To compile with the viewer I had to add this cmake module manually, with the following content:
OSG_FIND_PATH (OSGQT osgQt/GraphicsWindowQt)
OSG_FIND_LIBRARY(OSGQT osgQt)
FIND_PACKAGE_HANDLE_STANDARD_ARGS(osgQt DEFAULT_MSG
OSGQT_LIBRARY OSGQT_INCLUDE_DIR)