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

src/execution.cc

Index: src/execution.cc
diff --git a/src/execution.cc b/src/execution.cc
index f343868060da516624815c727dbe526ebc116c7a..025a25619f3f1fdbbd5f933b1471c6db56e5fa7c 100644
--- a/src/execution.cc
+++ b/src/execution.cc
@@ -502,7 +502,7 @@ void StackGuard::Continue(InterruptFlag after_what) {
 
 char* StackGuard::ArchiveStackGuard(char* to) {
   ExecutionAccess access(isolate_);
-  memcpy(to, reinterpret_cast<char*>(&thread_local_), sizeof(ThreadLocal));
+  OS::MemCopy(to, reinterpret_cast<char*>(&thread_local_), sizeof(ThreadLocal));
   ThreadLocal blank;
 
   // Set the stack limits using the old thread_local_.
@@ -519,7 +519,8 @@ char* StackGuard::ArchiveStackGuard(char* to) {
 
 char* StackGuard::RestoreStackGuard(char* from) {
   ExecutionAccess access(isolate_);
-  memcpy(reinterpret_cast<char*>(&thread_local_), from, sizeof(ThreadLocal));
+  OS::MemCopy(
+      reinterpret_cast<char*>(&thread_local_), from, sizeof(ThreadLocal));
   isolate_->heap()->SetStackLimits();
   return from + sizeof(ThreadLocal);
 }