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

[Joseph Huber via cfe-commits]

jhuber6 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.

Don't think so, should be handled here https://github.com/llvm/llvm-project/blob/e8b9e1354accf33ced45321abdd8c8bc65d025cc/clang/lib/Driver/Driver.cpp#L6436.

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