Fix the build on Mac.

src/serialize.cc

 // Copyright 2011 the V8 project authors. 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.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1140 matching lines @@
   isolate->set_serialize_partial_snapshot_cache_length(
       Isolate::kPartialSnapshotCacheCapacity);
 }
 
 
 void Serializer::VisitPointers(Object** start, Object** end) {
   Isolate* isolate = Isolate::Current();
 
   for (Object** current = start; current < end; current++) {
     if (start == isolate->heap()->roots_array_start()) {
-      root_index_wave_front_ = Max(root_index_wave_front_, current - start);
+      root_index_wave_front_ =
+          Max(root_index_wave_front_, static_cast<intptr_t>(current - start));
     }
     if (reinterpret_cast<Address>(current) ==
         isolate->heap()->store_buffer()->TopAddress()) {
       sink_->Put(kSkip, "Skip");
     } else if ((*current)->IsSmi()) {
       sink_->Put(kRawData, "RawData");
       sink_->PutInt(kPointerSize, "length");
       for (int i = 0; i < kPointerSize; i++) {
         sink_->Put(reinterpret_cast<byte*>(current)[i], "Byte");
       }
@@ skipping 453 matching lines @@
       fullness_[space] = RoundUp(fullness_[space], Page::kPageSize);
     }
   }
   int allocation_address = fullness_[space];
   fullness_[space] = allocation_address + size;
   return allocation_address;
 }
 
 
 } }  // namespace v8::internal