[LTO] Add debug logging for module ID <-> path mapping

[int3]

Summary

It's helpful

[kyulee]

llvm/lib/LTO/LTO.cpp

941

I don't think it matters too much as it's a debug code.
But if you hoist this code before readSummary above, you can get the module Id as below, and use it for both readSummary and this debug code.

uint64_t ModuleId = ThinLTO.ModuleMap.size();

[int3]

address comment

llvm/lib/LTO/LTO.cpp

for (const InputFile::Symbol &Sym : Syms) {
     if (!Sym.getIRName().empty()) {
       auto GUID = GlobalValue::getGUID(GlobalValue::getGlobalIdentifier(
           Sym.getIRName(), GlobalValue::ExternalLinkage, ""));
       if (Res.Prevailing)
         ThinLTO.PrevailingModuleForGUID[GUID] = BM.getModuleIdentifier();
     }
   }
 
+  uint64_t ModuleId = ThinLTO.ModuleMap.size();
   if (Error Err =
           BM.readSummary(ThinLTO.CombinedIndex, BM.getModuleIdentifier(),
-                         ThinLTO.ModuleMap.size(), [&](GlobalValue::GUID GUID) {
+                         ModuleId, [&](GlobalValue::GUID GUID) {
                            return ThinLTO.PrevailingModuleForGUID[GUID] ==
                                   BM.getModuleIdentifier();
                          }))
     return Err;
+  LLVM_DEBUG(dbgs() << "Module " << ModuleId << ": " << BM.getModuleIdentifier()
+                    << "\n");
 
   for (const InputFile::Symbol &Sym : Syms) {
     assert(ResI != ResE);
     SymbolResolution Res = *ResI++;
 
     if (!Sym.getIRName().empty()) {
       auto GUID = GlobalValue::getGUID(GlobalValue::getGlobalIdentifier(
           Sym.getIRName(), GlobalValue::ExternalLinkage, ""));
       if (Res.Prevailing) {
         assert(ThinLTO.PrevailingModuleForGUID[GUID] ==
                BM.getModuleIdentifier());