X64: Disabled RSet in 64-bit mode.

src/v8threads.cc

Index: src/v8threads.cc
diff --git a/src/v8threads.cc b/src/v8threads.cc
index 838cae772dcd1422050704e2cb69c21a9cb3bc6c..c5fc9fa7e6a4266322193654f0e8aefb45ffb93c 100644
--- a/src/v8threads.cc
+++ b/src/v8threads.cc
@@ -261,6 +261,8 @@ void ThreadManager::EagerlyArchiveThread() {
   ThreadState* state = lazily_archived_thread_state_;
   state->LinkInto(ThreadState::IN_USE_LIST);
   char* to = state->data();
+  // Ensure that data containing GC roots are archived first, and handle them
+  // in ThreadManager::Iterate(ObjectVisitor*).
   to = HandleScopeImplementer::ArchiveThread(to);
   to = Top::ArchiveThread(to);
 #ifdef ENABLE_DEBUGGER_SUPPORT