[clang] [AMDGPU] Use the AMDGPUToolChain when targeting C/C++ directly (PR #99687)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> Also, apparently there's some driver tests that expect `--target=amdgcn-amd-amdhsa-opencl` as the environment type. Is that the expected way to specify OpenCL? I'm not overly familiar.
> 

That was a mistake from long ago we shouldn't continue. A language is not an environment 

https://github.com/llvm/llvm-project/pull/99687