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

[Tex Riddell via llvm-commits]

tex3d wrote:

@VyacheslavLevytskyy: It looks like this PR failed to remove [the XFAIL added to the test](https://github.com/llvm/llvm-project/commit/c7e14689dd8bdf4b18dccb18895a9b80c225dc53) when fixing the issue.  We are hitting an unexpected pass causing testing to fail in our pipeline now due to this.

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