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

[Matt Arsenault via cfe-commits]

arsenm wrote:

I skimmed clover and I'm not sure it's even using the clang driver. It seems to be doing its own thing and directly using CompilerInstance

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