[dsymutil] Fix spurious warnings for missing symbols with thinLTO

[JDevlieghere]

Summary

Fix spurious warnings for missing symbols with thinLTO. The latter appends a unique suffix to avoid collisions for exported private symbols, resulting in dsymutil complaining it couldn't find the symbol in the object file.

rdar://75434058

llvm/test/tools/dsymutil/X86/thinlto.test

+$ cat foo.cpp
+struct nontrivial {
+  nontrivial() { }
+};
+
+void function2()
+{
+  static const nontrivial magic_static;
+}
+
+$ cat bar.cpp
+void function2();
+
+void function1()
+{
+  function2();
+}
+
+$ xcrun clang++ -g -flto=thin -O2 foo.cpp bar.cpp -c
+$ xcrun clang++ -flto=thin foo.o bar.o -Xlinker -object_path_lto -Xlinker lto -shared -o foobar.dylib
+
+RUN: dsymutil -oso-prepend-path %p/../Inputs %p/../Inputs/private/tmp/thinlto/foobar.dylib -o %t.dSYM 2>&1 | FileCheck %s --allow-empty
+CHECK-NOT: could not find object file symbol for symbol __ZZ9function2vE12magic_static
+CHECK-NOT: could not find object file symbol for symbol __ZGVZ9function2vE12magic_static

llvm/tools/dsymutil/MachODebugMapParser.cpp

void MachODebugMapParser::handleStabSymbolTableEntry(uint32_t StringIndex,
   if (ObjectSymIt == CurrentObjectAddresses.end() && Type != MachO::N_STSYM) {
     for (const auto &Alias : getMainBinarySymbolNames(Value)) {
       ObjectSymIt = CurrentObjectAddresses.find(Alias);
       if (ObjectSymIt != CurrentObjectAddresses.end())
         break;
     }
   }
 
+  // ThinLTO adds a unique suffix to exported private symbols.
+  for (auto Iter = CurrentObjectAddresses.begin();
+       Iter != CurrentObjectAddresses.end(); ++Iter) {
+    llvm::StringRef SymbolName = Iter->getKey();
+    auto Pos = SymbolName.rfind(".llvm.");
+    if (Pos != llvm::StringRef::npos && SymbolName.substr(0, Pos) == Name) {
+      ObjectSymIt = Iter;
+      break;
+    }
+  }
+
   if (ObjectSymIt == CurrentObjectAddresses.end()) {
     Warning("could not find object file symbol for symbol " + Twine(Name));
     return;
   }
 
   if (!CurrentDebugMapObject->addSymbol(Name, ObjectSymIt->getValue(), Value,
                                         Size)) {
     Warning(Twine("failed to insert symbol '") + Name + "' in the debug map.");