[clang] [clang-tools-extra] Remove ^^ as a token in OpenCL (PR #108224)

[Anastasia Stulova via cfe-commits]

AnastasiaStulova wrote:

I think that the diagnostic change is reasonable. Clang doesn't support OpenCL C++ at present so we won't need to worry about it. However the mission of C++ for OpenCL is to track C++ and track OpenCL i.e. we may want to update to C++ with reflection. So it would be good to keep this as an option. But we don't have this plan right now.

So if we keep this as reserve identifier for C++ for OpenCL it is probably the best approach since if one day we decide to upgrade it to C++ with reflection the code using ``^^`` would not longer be invalid. Does it make sense? 

https://github.com/llvm/llvm-project/pull/108224