[clang] [llvm] [HLSL][SPIR-V] Implement vk::push_constant (PR #166793)

[Steven Perron via llvm-commits]

https://github.com/s-perron commented:

LGTM except I would like to see a test that checks that the AST is adding the attribute correctly.

Also, add a test for DXIL. Make sure it properly ignores the attribute.

https://github.com/llvm/llvm-project/pull/166793