Fix sign extension issue with clang/gcc

runtime/vm/snapshot.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/snapshot.h"
 
 #include "vm/assert.h"
 #include "vm/bootstrap.h"
 #include "vm/heap.h"
 #include "vm/object.h"
@@ skipping 239 matching lines @@
   // - Object that is seen for the first time (inlined as follows):
   //    (object size in multiples of kObjectAlignment | 0x1)
   //    serialized fields of the object
   //    ......
 
   NoGCScope no_gc;
   // writing a snap shot.
 
   // First check if it is a Smi (i.e not a heap object).
   if (!rawobj->IsHeapObject()) {
-    Write<int64_t>(reinterpret_cast<int64_t>(rawobj));
+    Write<int64_t>(reinterpret_cast<intptr_t>(rawobj));
     return;
   }
 
   // Check if it is a singleton null object which is shared by all isolates.
   if (rawobj == Object::null()) {
     WriteIndexedObject(Object::kNullObject);
     return;
   }
 
   // Check if it is a singleton sentinel object which is shared by all isolates.
@@ skipping 174 matching lines @@
 
 
 void SnapshotWriterVisitor::VisitPointers(RawObject** first, RawObject** last) {
   for (RawObject** current = first; current <= last; current++) {
     RawObject* raw_obj = *current;
     writer_->WriteObject(raw_obj);
   }
 }
 
 }  // namespace dart