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

[Joseph Huber via cfe-commits]

jhuber6 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.

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