VTK_USE_X=ON shouldn't be required to build ParaView GUI
Follows mail exchange with Utkarsh (Subject : OffScreen/OnScreen, Software/Hardware Rendering with EGL)
"VTK_USE_X is currently needed for the GUI. Although as I am thinking of this, with Qt 5, we can get rid of this requirement. You'll still need to X to use the GUI and for building Qt, but ParaView should not directly depend on X (unless I am missing something). Please report an issue for this, if you don't mind. We should investigate this." -- Utkarsh