[llvm-symbolizer] Add architecture fallback from x86_64h to x86_64

[kubamracek]

Summary

On OS X, x86_64h architecture can be mixed with x86_64 in a single process. When we try to symbolicate addresss from a sanitizer, llvm-symbolizer is called with --default-arch=x86_64h (when running on a Haswell+ machine). However, if a binary/library contains only the x86_64 slice, llvm-symbolizer simply fails. We should fallback from x86_64h to x86_64 if the x86_64h slice is not present.

[samsonov]

I don't see why this is correct place to fix it. If we can treat x86_64h as x86_64, then getOrCreateObjects should work correctly for it. Which means that getObjectFileFromBinary should work correctly for it. Which probably means that you need to teach MachOUniversalBinary::getObjectForArch() to return you slice for x86_64, if x86_64h is unavailable.

[kubamracek]

llvm-symbolizer already supports specifying the arch with a colon ("mymodule.dylib:x86_64h").

lib/DebugInfo/Symbolize/Symbolize.cpp

if (ColonPos != std::string::npos) {
     if (Triple(ArchStr).getArch() != Triple::UnknownArch) {
       BinaryName = ModuleName.substr(0, ColonPos);
       ArchName = ArchStr;
     }
   }
   auto ObjectsOrErr = getOrCreateObjects(BinaryName, ArchName);
   if (auto EC = ObjectsOrErr.getError()) {
     // Failed to find valid object file.
+    // For x86_64h, fallback to x86_64.
+    if (ArchName == "x86_64h") {
+      ObjectsOrErr = getOrCreateObjects(BinaryName, "x86_64");
+      if (auto EC = ObjectsOrErr.getError()) {
         Modules.insert(std::make_pair(ModuleName, EC));
         return EC;
       }
+    } else {
+      Modules.insert(std::make_pair(ModuleName, EC));
+      return EC;
+    }
+  }
   ObjectPair Objects = ObjectsOrErr.get();
 
   std::unique_ptr<DIContext> Context;
   if (auto CoffObject = dyn_cast<COFFObjectFile>(Objects.first)) {
     // If this is a COFF object, assume it contains PDB debug information.  If
     // we don't find any we will fall back to the DWARF case.
     std::unique_ptr<IPDBSession> Session;
     PDB_ErrorCode Error = loadDataForEXE(PDB_ReaderType::DIA,