[clang] [Clang] Permit `vulkan` as an OS for the SPIRV target architecture (PR #196101)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> The change looks good to me, with one note: per my understanding 'vulkan', 'vulkan1.2' and 'vulkan1.3' are effectively all different OSes from target triple perspective. If my understanding is correct - these OSes should also be accounted for in the PR.

I don't think there's such a distinction on the OS level. There's no way to specify that as a Triple.

https://github.com/llvm/llvm-project/pull/196101