Fix getSourceLanguage build after llvm commit 6cba572 (#3385)

getSourceLanguage API is changed to return DISourceLanguageName in
llvm/llvm-project@6cba572d9efe

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@daba8b217bc2668

Author: wenju-he

llvm-spirv/lib/SPIRV/LLVMToSPIRVDbgTran.cpp

@@ -587,8 +587,8 @@ SPIRVEntry *LLVMToSPIRVDbgTran::transDbgCompileUnit(const DICompileUnit *CU) {
   if (isNonSemanticDebugInfo())
     generateBuildIdentifierAndStoragePath(CU);
 
-  auto DwarfLang =
-      static_cast<llvm::dwarf::SourceLanguage>(CU->getSourceLanguage());
+  auto DwarfLang = static_cast<llvm::dwarf::SourceLanguage>(
+      CU->getSourceLanguage().getUnversionedName());
   Ops[LanguageIdx] =
       BM->getDebugInfoEIS() == SPIRVEIS_NonSemantic_Shader_DebugInfo_200
           ? convertDWARFSourceLangToSPIRVNonSemanticDbgInfo(DwarfLang)