Really really fix mac x64 debug build by using more fixed-length encoding and long jumps.

runtime/vm/stub_code_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"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
@@ skipping 1088 matching lines @@
       __ leaq(RCX, FieldAddress(RAX, Instance::NextFieldOffset()));
       // Loop until the whole object is initialized.
       // RAX: new object (tagged).
       // RBX: next object start.
       // RCX: next word to be initialized.
       // RDX: new object type arguments (if is_cls_parameterized).
       Label init_loop;
       Label done;
       __ Bind(&init_loop);
       __ cmpq(RCX, RBX);
-      __ j(ABOVE_EQUAL, &done, Assembler::kNearJump);
+#if defined(DEBUG)
+      static const bool kJumpLength = Assembler::kFarJump;
+#else
+      static const bool kJumpLength = Assembler::kNearJump;
+#endif  // DEBUG
+      __ j(ABOVE_EQUAL, &done, kJumpLength);
       __ InitializeFieldNoBarrier(RAX, Address(RCX, 0), R12);
       __ addq(RCX, Immediate(kWordSize));
       __ jmp(&init_loop, Assembler::kNearJump);
       __ Bind(&done);
     }
     if (is_cls_parameterized) {
       // RDX: new object type arguments.
       // Set the type arguments in the new object.
       intptr_t offset = cls.type_arguments_field_offset();
       __ InitializeFieldNoBarrier(RAX, FieldAddress(RAX, offset), RDX);
@@ skipping 968 matching lines @@
 
   __ movq(left, Address(RSP, 2 * kWordSize));
   __ movq(right, Address(RSP, 1 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64