[clang] [llvm] Make OpenCL an OSType rather than an EnvironmentType. (PR #170297)

[Alexey Bader via llvm-commits]

bader wrote:

> OpenCL should be neither an operating system or an environment. It's a source language, not a target ABI. I think we used to mishandle HIP and OpenCL differences and I don't think AMD is using this anymore

There must be some feature to separate GPU code execution environments (e.g. OpenCL and Vulkan). @arsenm, do you have a constructive proposal to separate them?

https://github.com/llvm/llvm-project/pull/170297