[llvm] Add assertions for the smart pointers with the possibility to be null in DWARFLinker::loadClangModule

[OikawaKirie]

Summary

Split from D91844.

The local variable Unit in function DWARFLinker::loadClangModule in file llvm/lib/DWARFLinker/DWARFLinker.cpp. If the variable is not set in the loop below its definition, it will trigger a null pointer dereference after the loop.

[avl]

LGTM.

[OikawaKirie]

If the revision is done, please commit it on my behalf. Thank you.

Ella Ma <[e-mail]>

llvm/lib/DWARFLinker/DWARFLinker.cpp

if (!registerModuleReference(CUDie, *CU, File, StringPool, ODRContexts,
                          ModulesEndOffset, Options.ParseableSwiftInterfaces,
                          [&](const Twine &Warning, const DWARFDie &DIE) {
                            reportWarning(Warning, File, &DIE);
                          });
       // Keep everything.
       Unit->markEverythingAsKept();
     }
   }
+  assert(Unit && "CompileUnit is not set!");
   if (!Unit->getOrigUnit().getUnitDIE().hasChildren())
     return Error::success();
   if (!Quiet && Options.Verbose) {
     outs().indent(Indent);
     outs() << "cloning .debug_info from " << Filename << "\n";
   }
 
   UnitListTy CompileUnits;