message: add check in the superbuild for using a 32-bit build
diff: @@ -21,6 +21,15 @@ endif()
  project(OSPRay_superbuild)
  +if(CMAKE_SIZEOF_VOID_P EQUAL 4)
  + message(FATAL_ERROR "OSPRay can only be built on 64-bit platforms. This
  + problem most commonly happens on Windows, where the right solution is to
  + switch to a 64-bit generator: retry running CMake with '-G \"Visual
  + Studio 15 2017 Win64\"'")
  +else()
  + message(STATUS "Proceeding with a 64-bit generator. (${CMAKE_SIZEOF_VOID_P})")
  +endif()
  +
  include(ExternalProject)
  include(GNUInstallDirs)
  include(ProcessorCount)
  