[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:

> > 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.
> 
> If it's just until we fix upstream, I'd be in favor of an XFAIL.
> 
> > 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).
> 
> What do you mean by that?

Please see https://llvm.org/docs/doxygen/SPIRVInstructionSelector_8cpp_source.html line 1772, the comment is "// OpenCL uses nulls for Zero. In HLSL we don't use null constants.", and the whole thing about `bool ZeroAsNull` in SPIRVInstructionSelector.cpp

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