Fix mac x64 debug build by using fixed-length encoding.

runtime/vm/assembler_x64.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 "vm/globals.h"  // NOLINT
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/heap.h"
@@ skipping 3068 matching lines @@
   j(EQUAL, &ok, Assembler::kNearJump);
   Stop("Expected zapped, Smi or null");
   Bind(&ok);
 }
 
 
 void Assembler::VerifySmi(const Address& dest, const char* stop_msg) {
   Label done;
   testb(dest, Immediate(kHeapObjectTag));
   j(ZERO, &done, Assembler::kNearJump);
-  Stop(stop_msg);
+  static const bool kFixedLengthEncoding = true;
+  Stop(stop_msg, kFixedLengthEncoding);
   Bind(&done);
 }
 #endif  // defined(DEBUG)
 
 
 void Assembler::StoreIntoObject(Register object,
                                 const Address& dest,
                                 Register value,
                                 bool can_value_be_smi) {
   ASSERT(object != value);
@@ skipping 899 matching lines @@
 
 
 const char* Assembler::FpuRegisterName(FpuRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfXmmRegisters));
   return xmm_reg_names[reg];
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64