[clang] [clang][Driver][HIP] Add support for mixing AMDGCNSPIRV & concrete `offload-arch`s. (PR #113509)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 approved this pull request.

I guess this is good for now, but we really need to work with how to actually handle multiple toolchains at once.

https://github.com/llvm/llvm-project/pull/113509