CL: sync C & C++ headers with Khronos
C headers from https://github.com/KhronosGroup/OpenCL-Headers at commit 0d5f18c6e7196863bc1557a693f1509adfcee056
C++ headers from https://github.com/KhronosGroup/OpenCL-CLHPP at commit cf9fc1035e8298c7ce65ee33066a660fd9892ebb
Intel CI run to make sure nothing's subtly broken by the alignment changes in the C headers.