Quick and dirty fix for g++-6, which does not work with -isystem https://bugreports.qt.io/browse/QTBUG-53375, https://codereview.qt-project.org/#/c/159215 ===================================================================
patched src/sketch/zoomablegraphicsview.cpp to prevent calling QWheelEvent::device, which is not implemented in Qt 5.15 ===================================================================