This fixes a number of things that are warnings in the Mac compiler....

core/cross/message_queue.cc

 /*
  * Copyright 2009, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 278 matching lines @@
   }
 
 #if defined(OS_MACOSX) | defined(OS_LINUX)
   if (message_length == 0) {  // EOF
     *length = 0;
     return true;
   }
 #endif
 
   // Valid messages must always contain at least the ID of the message
-  if (message_length >= sizeof(*message_id)) {
+  if (message_length >= static_cast<int>(sizeof(*message_id))) {
     // Check if the incoming message requires more space than we have
     // currently allocated.
     if (header->flags & nacl::kMessageTruncated) {
       LOG(ERROR) << "Incoming message was truncated";
       return false;
     }
 
     // Extract the ID of the message just received.
     MessageId id_found = *(reinterpret_cast<MessageId*>(header->iov[0].base));
     if (id_found <= INVALID_ID || id_found >= MAX_NUM_IDS) {
@@ skipping 265 matching lines @@
   memcpy(texture_data, target_address, number_of_bytes);
 
   texture_object->Unlock(level);
 
   SendBooleanResponse(client->client_handle(), true);
   return true;
 }
 
 
 }  // namespace o3d