message: make OSPRAY_SDK_USE_FILE more robust for downstream projects
diff: @@ -13,7 +13,15 @@ include(ispc)
  message(STATUS "Using found OSPRay ISA targets: ${OSPRAY_ISPC_TARGET_LIST}")
  +if (NOT TARGET openvkl::openvkl OR NOT TARGET embree)
  + message(FATAL_ERROR "OSPRay pre-built binary redistributables cannot be
  + extended with the SDK. Please build OSPRay from source to enable extending
  + OSPRay!")
  +endif()
  +
  ispc_include_directories(
  ${OSPRAY_INCLUDE_DIR}
  ${OSPRAY_INCLUDE_DIR}/ospray/SDK
  + ${EMBREE_INCLUDE_DIRS}
  + ${OPENVKL_INCLUDE_DIRS}
  )
  