Make Android gyp flags more like Linux gyp flags. Fix cases of -Wconversion-null.

runtime/vm/simulator_arm64.cc

 // Copyright (c) 2014, 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_ARM64)
 
@@ skipping 1200 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::ReadExclusiveX(uword addr, Instr* instr) {
   MutexLocker ml(exclusive_access_lock_);
   SetExclusiveAccess(addr);
   return ReadX(addr, instr);
 }
 
 
@@ skipping 2373 matching lines @@
   set_register(NULL, kExceptionObjectReg, bit_cast<int64_t>(raw_exception));
   set_register(NULL, kStackTraceObjectReg, bit_cast<int64_t>(raw_stacktrace));
   buf->Longjmp();
 }
 
 }  // namespace dart
 
 #endif  // !defined(USING_SIMULATOR)
 
 #endif  // defined TARGET_ARCH_ARM64