[llvm] [SPIR-V] Fix DebugScope resolving DILexicalBlockFile to DebugCompilationUnit (PR #228259)

[Manuel Carrasco via llvm-commits]

mgcarrasco wrote:

> This emitted a DebugScope referencing DebugCompilationUnit instead of DebugFunction, producing malformed SPIR-V that crashed IGC during program compilation.

This is still legal SPIRV, although the fix makes sense to me. I think IGC should not have crashed either way. 

https://github.com/llvm/llvm-project/pull/228259