The Geant4 cmake check requires Qt5OpenGL_FOUND, so we must require
the Qt5 +opengl variant. If not, the cmake phase fall through to Qt4
and fails due to a missing Qt4::QtGui target.
In Geant4InterfaceOptions.cmake:
```
if(Qt5Core_FOUND
AND Qt5Gui_FOUND
AND Qt5Widgets_FOUND
AND Qt5OpenGL_FOUND
AND Qt5PrintSupport_FOUND)
```
Ref: https://github.com/Geant4/geant4/blob/master/cmake/Modules/Geant4InterfaceOptions.cmake#L90
(5baee230e93612916bcea11ebf822756cfa7282c, Import Geant4 10.6.0 source tree)