[dsymutil] Fix data race in input verification (NFC)

Dump verification errors to a local buffer instead of racing stdio and
potentially showing interleaved output.

(cherry picked from commit 4d1d8a8)

Author: JDevlieghere

llvm/include/llvm/DWARFLinker/DWARFLinker.h

@@ -357,7 +357,7 @@ class DWARFLinker {
     Pub,       ///< .debug_pubnames, .debug_pubtypes
     DebugNames ///< .debug_names.
   };
-  typedef std::function<void(const DWARFFile &File)> inputVerificationHandler;
+  typedef std::function<void(const DWARFFile &File, llvm::StringRef Output)> inputVerificationHandler;
   typedef std::function<ErrorOr<DWARFFile &>(StringRef ContainerName,
                                              StringRef Path)>
       objFileLoader;

llvm/include/llvm/DWARFLinkerParallel/DWARFLinker.h

@@ -134,7 +134,7 @@ class DWARFLinker {
       const Twine &Warning, StringRef Context, const DWARFDie *DIE)>;
   using ObjFileLoaderTy = std::function<ErrorOr<DWARFFile &>(
       StringRef ContainerName, StringRef Path)>;
-  using InputVerificationHandlerTy = std::function<void(const DWARFFile &File)>;
+  using InputVerificationHandlerTy = std::function<void(const DWARFFile &File, llvm::StringRef Output)>;
   using ObjectPrefixMapTy = std::map<std::string, std::string>;
   using CompileUnitHandlerTy = function_ref<void(const DWARFUnit &Unit)>;
   using TranslatorFuncTy = std::function<StringRef(StringRef)>;

llvm/lib/DWARFLinker/DWARFLinker.cpp

@@ -3037,11 +3037,13 @@ Error DWARFLinker::cloneModuleUnit(LinkContext &Context, RefModuleUnit &Unit,
 void DWARFLinker::verifyInput(const DWARFFile &File) {
   assert(File.Dwarf);
 
-  raw_ostream &os = Options.Verbose ? errs() : nulls();
+
+  std::string Buffer;
+  raw_string_ostream OS(Buffer);
   DIDumpOptions DumpOpts;
-  if (!File.Dwarf->verify(os, DumpOpts.noImplicitRecursion())) {
+  if (!File.Dwarf->verify(OS, DumpOpts.noImplicitRecursion())) {
     if (Options.InputVerificationHandler)
-      Options.InputVerificationHandler(File);
+      Options.InputVerificationHandler(File, OS.str());
   }
 }
 

llvm/tools/dsymutil/DwarfLinkerForBinary.cpp

@@ -689,8 +689,11 @@ bool DwarfLinkerForBinary::linkImpl(
   GeneralLinker->setNumThreads(Options.Threads);
   GeneralLinker->setPrependPath(Options.PrependPath);
   GeneralLinker->setKeepFunctionForStatic(Options.KeepFunctionForStatic);
-  GeneralLinker->setInputVerificationHandler([&](const OutDwarfFile &File) {
-    reportWarning("input verification failed", File.FileName);
+  GeneralLinker->setInputVerificationHandler([&](const OutDwarfFile &File, llvm::StringRef Output) {
+    std::lock_guard<std::mutex> Guard(ErrorHandlerMutex);
+    if (Options.Verbose)
+      errs() << Output;
+    warn("input verification failed", File.FileName);
     HasVerificationErrors = true;
   });
   auto Loader = [&](StringRef ContainerName,