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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

I feel like we should treat `spirv` in the same way we handle stuff like `sm_90` in the `CudaArch` enum. (We should probably also rename that as it's used for generic offloading now). OpenMP infers the triple from the arch, so in the future when OpenMP can handle SPIR-V we can simply re-use that.

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