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

[Matt Arsenault via cfe-commits]

arsenm wrote:

> > Does this change the behavior with amdgcn-- or amdgcn-mesa-mesa3d?
> 
> Those both use the `AMDGPUToolChain`. I suppose you could make the argument that `--target=amdgcn--` is the intended target for "standalone amd" stuff.

Mostly I'm just wondering if it breaks whatever clover is doing. 

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