[clang] Add SPIRV support to HIPAMD toolchain (PR #75357)

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

> > Is generic the best name here? I feel like that's going to be heavily overloaded. I'd much prefer a new architecture that just treats "SPIR-V" as a single architecture. E.g. `--offload-arch=spirv` or something.

For HIPAMD toolchain, `--offload-arch=generic` and `--offload-arch=spirv` does not make much difference. However, I understand `--offload-arch=generic` is probably too ambiguous and `--offload-arch=spirv` is better. I can change it to `spirv`.

https://github.com/llvm/llvm-project/pull/75357