Fix Android build warnings

runtime/vm/simulator_arm.cc

 // Copyright (c) 2013, 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 <setjmp.h>  // NOLINT
 #include <stdlib.h>
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM)
 
@@ skipping 1119 matching lines @@
       exclusive_access_state_[i].addr = 0;
     }
   }
   return result;
 }
 
 
 void Simulator::ClearExclusive() {
   MutexLocker ml(exclusive_access_lock_);
   // Remove the reservation for this thread.
-  SetExclusiveAccess(NULL);
+  SetExclusiveAccess(0);
 }
 
 
 intptr_t Simulator::ReadExclusiveW(uword addr, Instr* instr) {
   MutexLocker ml(exclusive_access_lock_);
   SetExclusiveAccess(addr);
   return ReadW(addr, instr);
 }
 
 
@@ skipping 2757 matching lines @@
   set_register(kExceptionObjectReg, bit_cast<int32_t>(raw_exception));
   set_register(kStackTraceObjectReg, bit_cast<int32_t>(raw_stacktrace));
   buf->Longjmp();
 }
 
 }  // namespace dart
 
 #endif  // defined(USING_SIMULATOR)
 
 #endif  // defined TARGET_ARCH_ARM