Attempting to fix compiler error on Mac with Clang.
Attempting to fix compiler error on Mac with Clang.

There seems to be a missing case that leaves some macros
undefined. Attempting to fix.

keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix