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

src/global-handles.h

Index: src/global-handles.h
diff --git a/src/global-handles.h b/src/global-handles.h
index ffec6c20445f4abe9258b5c95024d17e2e9ea7f1..6289782a0a7d1e53c46f2f08b38ebc81139079e5 100644
--- a/src/global-handles.h
+++ b/src/global-handles.h
@@ -93,7 +93,7 @@ class ImplicitRefGroup {
         malloc(OFFSET_OF(ImplicitRefGroup, children_[length])));
     group->parent_ = parent;
     group->length_ = length;
-    CopyWords(group->children_, children, static_cast<int>(length));
+    CopyWords(group->children_, children, length);
     return group;
   }