OpenCL 1.2 deprecation warnings

There's currently two deprecation warnings with OpenCL 1.2 with latest Khronos' headers

* enqueueMarker
  - this is deprecated and I believe enqueueMarkerWithWaitList is supposed to replace it
  - however, there the Khronos' header has a mistake where enqueueMarkerWithWaitList can     be made const like enqueueMarker

* __local
  - lots of warnings about using __local instead of the newer local, but I cannot think of a clean way of supporting both

There is no urgency with these changes on my end - but it would be nice to get rid of the warnings.