In the meantime I tried a vanilla configure without any of my options. It seems that I can only set VTK_OPENGL_HAS_OSMESA, but the other two options I used from 8.2 are not available in ccmake advanced mode (OSMESA_INCLUDE_DIR and OSMESA_LIBRARY). I only find OPENGL_xmesa_INCLUDE_DIR OPENGL_xmesa_INCLUDE_DIR-NOTFOUND.
Am I using some deprecated variables here? Maybe I should provide the mesa installation location differently?