The C++ for OpenCL programming language and OpenCL C language extensions are already supported by Clang! Please refer to the official Clang documentation for more details on how to use the new language mode and for the information about the implementation status.
LLVM Clang 9.0 has been released and is now available for download. This is the first release to contain experimental support of C++ for OpenCL language mode in Clang. More details can be found in the Clang documentation. This new support will be discussed at the LLVM Developers meeting (October 2019) at the From C++ for OpenCL to C++ for accelerator devices talk by Khronos Member Anastasia Stulova.