message: Newer clang discourages alloca; workaround
diff: -## Copyright 2009-2019 Intel Corporation
  +## Copyright 2009-2020 Intel Corporation
  ## SPDX-License-Identifier: Apache-2.0
  set(OSPRAY_CXX_FLAGS "-fno-strict-aliasing -Wno-narrowing")
  @@ -44,6 +44,7 @@ if(OSPRAY_STRICT_BUILD)
  set(OSPRAY_CXX_FLAGS "-Wno-cast-qual ${OSPRAY_CXX_FLAGS}") #Embree v3.x issue
  set(OSPRAY_CXX_FLAGS "-Wno-extra-semi-stmt ${OSPRAY_CXX_FLAGS}")
  set(OSPRAY_CXX_FLAGS "-Wno-shadow-field ${OSPRAY_CXX_FLAGS}")
  + set(OSPRAY_CXX_FLAGS "-Wno-alloca ${OSPRAY_CXX_FLAGS}")
  # Options selected for Clang 5.0+
  set(OSPRAY_CXX_FLAGS "-Weverything ${OSPRAY_CXX_FLAGS}")
  