[clang] [llvm] [HLSL] Implement ddx/ddy_fine intrinsics (PR #168874)

[Alexander Johnston via llvm-commits]

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Alexander-Johnston wrote:

I think we should be able to get the SM and stage during the frontend. I can write a patch to cover each of the derivative instructions at once, but similar to above, should that check just be doing the pixel stage for now and the other stages handled in another PR along with the implementations?
Thanks!

https://github.com/llvm/llvm-project/pull/168874