[llvm] [clang] [HLSL][SPIR-V] Add Vulkan to target triple (PR #76749)

[Natalie Chouinard via cfe-commits]

sudonatalie wrote:

Rebased due to conflicts. I'm going to go ahead and merge this today to make the next dependent change easier to review, but DXIL folks please still feel free to follow-up if there are any concerns.

(Also, ignoring the code formatter bot since it seems to be an existing intentional formatting choice in the file that doesn't play nicely with clang-format yet)

https://github.com/llvm/llvm-project/pull/76749