apple: bundle ITK only when it is enabled in the superbuild
apple: bundle ITK only when it is enabled in the superbuild

cjh1/tomviz-superbuild,mathstuf/tomviz-superbuild,mathstuf/tomviz-superbuild,mathturtle/tomviz-superbuild,OpenChemistry/tomviz-superbuild,cjh1/tomviz-superbuild,mathturtle/tomviz-superbuild,OpenChemistry/tomviz-superbuild