[llvm] [SPIR-V] Emit OpConstant instead of OpConstantNull to conform to NonSemantic.Shader.DebugInfo.100 DebugTypeBasic's flags definition (PR #118333)

[Vyacheslav Levytskyy via llvm-commits]

VyacheslavLevytskyy wrote:

> I'm fine with this PR, but we talked a bit about this issue internally, and we believe this is not a bug in LLVM. It looks like a simple spirv-val oversight. I'll ping Alan on the verifier bit see if we can move forward with a fix in spirv-val instead.

Thank you, I also think that this should be fixed on spirv-val side. However, until it is fixed we should either proceed with this PR or add XFAIL to the test case. Also, as a side note, I guess we will anyway need to figure out OpConstant vs. OpConstantNull in debug-info to account for environments without null constants (HLSL).

https://github.com/llvm/llvm-project/pull/118333