message: set predefined values for OSPRAY_ISPC_ADDRESSING, validate it if incorrect
diff: @@ -68,8 +68,14 @@ IF(NOT ISPC_VERSION)
  ENDIF()
  SET(OSPRAY_ISPC_ADDRESSING 32 CACHE INT "32 vs 64 bit addressing in ispc")
  +SET_PROPERTY(CACHE OSPRAY_ISPC_ADDRESSING PROPERTY STRINGS 32 64)
  MARK_AS_ADVANCED(OSPRAY_ISPC_ADDRESSING)
  +IF (NOT (OSPRAY_ISPC_ADDRESSING STREQUAL "32" OR
  + OSPRAY_ISPC_ADDRESSING STREQUAL "64"))
  + MESSAGE(FATAL_ERROR "OSPRAY_ISPC_ADDRESSSING must be set to either '32' or '64'!")
  +ENDIF()
  +
  GET_FILENAME_COMPONENT(ISPC_DIR ${ISPC_EXECUTABLE} PATH)
  