Replace OS::MemCopy with OS::MemMove (just as fast but more flexible).

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index cd6ee4756976ba8502117bdc0168168a5f513805..675d5be9b1cd4d836ec1ac19537457ee7194ebd1 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1562,8 +1562,8 @@ Handle<Context> Isolate::GetCallingNativeContext() {
 
 
 char* Isolate::ArchiveThread(char* to) {
-  memcpy(to, reinterpret_cast<char*>(thread_local_top()),
-         sizeof(ThreadLocalTop));
+  OS::MemCopy(to, reinterpret_cast<char*>(thread_local_top()),
+              sizeof(ThreadLocalTop));
   InitializeThreadLocal();
   clear_pending_exception();
   clear_pending_message();
@@ -1573,8 +1573,8 @@ char* Isolate::ArchiveThread(char* to) {
 
 
 char* Isolate::RestoreThread(char* from) {
-  memcpy(reinterpret_cast<char*>(thread_local_top()), from,
-         sizeof(ThreadLocalTop));
+  OS::MemCopy(reinterpret_cast<char*>(thread_local_top()), from,
+              sizeof(ThreadLocalTop));
   // This might be just paranoia, but it seems to be needed in case a
   // thread_local_top_ is restored on a separate OS thread.
 #ifdef USE_SIMULATOR