[clang] [llvm] [DirectX][DXIL] Set DXIL Version in DXIL target triple based on shader model version (PR #90809)

[Chris B via cfe-commits]

https://github.com/llvm-beanz commented:

Given that @bogner had concerns about the other approach I think we should get him to review this before moving forward.

That said, other than some missing unit test coverage I think this approach looks fine.

https://github.com/llvm/llvm-project/pull/90809