Fix MacOSX build error related to OpenGL2/vtkOpenGL.h. See #15285
Fix MacOSX build error related to OpenGL2/vtkOpenGL.h. See #15285

This commit ensures the file defining VTK_USE_{CARBON|COCOA} is included
and fixes the following build error caught by Slicer dashboard:

// ---------
In file included from /Users/kitware/Dashboards/Experimental/Slicer-0/Modules/Loadable/VolumeRendering/VolumeRenderingReplacements/vtkSlicerOpenGLRayCastImageDisplayHelper.cxx:25:
/Users/kitware/Dashboards/Experimental/Slicer-0-build/VTKv6/Rendering/OpenGL2/vtkOpenGL.h:26:11: fatal error: 'GL/gl.h' file not found

          ^
1 error generated.
// ---------

Change-Id: I34b62ab1ab6954ebba6ca91b6c99dd00b30f1957

jmerkow/VTK,keithroe/vtkoptix,sankhesh/VTK,keithroe/vtkoptix,keithroe/vtkoptix,hendradarwin/VTK,sankhesh/VTK,SimVascular/VTK,candy7393/VTK,gram526/VTK,jmerkow/VTK,demarle/VTK,demarle/VTK,demarle/VTK,candy7393/VTK,sumedhasingla/VTK,gram526/VTK,sankhesh/VTK,mspark93/VTK,demarle/VTK,msmolens/VTK,candy7393/VTK,ashray/VTK-EVM,demarle/VTK,msmolens/VTK,ashray/VTK-EVM,SimVascular/VTK,gram526/VTK,SimVascular/VTK,jmerkow/VTK,jmerkow/VTK,sumedhasingla/VTK,sankhesh/VTK,sumedhasingla/VTK,hendradarwin/VTK,jmerkow/VTK,candy7393/VTK,jmerkow/VTK,jmerkow/VTK,jmerkow/VTK,msmolens/VTK,SimVascular/VTK,gram526/VTK,sumedhasingla/VTK,hendradarwin/VTK,SimVascular/VTK,candy7393/VTK,sankhesh/VTK,ashray/VTK-EVM,keithroe/vtkoptix,keithroe/vtkoptix,gram526/VTK,sankhesh/VTK,keithroe/vtkoptix,hendradarwin/VTK,mspark93/VTK,SimVascular/VTK,mspark93/VTK,sumedhasingla/VTK,sankhesh/VTK,candy7393/VTK,mspark93/VTK,sumedhasingla/VTK,gram526/VTK,msmolens/VTK,candy7393/VTK,ashray/VTK-EVM,msmolens/VTK,msmolens/VTK,sumedhasingla/VTK,ashray/VTK-EVM,demarle/VTK,ashray/VTK-EVM,ashray/VTK-EVM,sankhesh/VTK,msmolens/VTK,hendradarwin/VTK,mspark93/VTK,mspark93/VTK,demarle/VTK,gram526/VTK,demarle/VTK,mspark93/VTK,keithroe/vtkoptix,candy7393/VTK,ashray/VTK-EVM,SimVascular/VTK,hendradarwin/VTK,hendradarwin/VTK,SimVascular/VTK,msmolens/VTK,gram526/VTK,mspark93/VTK,sumedhasingla/VTK,keithroe/vtkoptix