message: don't warn about unknown (clang) pragmas when using icc
diff: ## limitations under the License. ##
  ## ======================================================================== ##
  -SET(OSPRAY_CXX_FLAGS "-std=c++11 -fPIC -fno-strict-aliasing -no-ansi-alias -DNOMINMAX")
  +SET(OSPRAY_CXX_FLAGS "-std=c++11 -fPIC -fno-strict-aliasing -no-ansi-alias -DNOMINMAX -Wno-unknown-pragmas")
  IF(OSPRAY_STRICT_BUILD)
  SET(OSPRAY_CXX_FLAGS "-Wall ${OSPRAY_CXX_FLAGS}")
  