message: Enable format macros in glTFViewer
  Without this compilation can fail in picojson.h because the PRId64 macro
  isn't defined (it is used to print 64bit ints).
diff: // See the License for the specific language governing permissions and
  // limitations under the License.
  +// Enable this before including any headers as we want inttypes.h to define
  +// format macros such as PRId64 that are used in picojson.
  +#ifndef __STDC_FORMAT_MACROS
  +#define __STDC_FORMAT_MACROS
  +#endif
  +
  #include "Utils.h"
  #include <bitset>
  