Fix XCode build.

src/arm/virtual-frame-arm.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 544 matching lines @@
   switch (top_of_stack_state_) {
     case NO_TOS_REGISTERS:
     case R0_TOS:
     case R0_R1_TOS:
       MergeTOSTo(R0_R1_TOS);
       return r1;
     case R1_TOS:
     case R1_R0_TOS:
       MergeTOSTo(R1_R0_TOS);
       return r0;
+    default:
+      UNREACHABLE();
+      return no_reg;
   }
-  UNREACHABLE();
-  return no_reg;
 }
 
 
 void VirtualFrame::Dup() {
   if (SpilledScope::is_spilled()) {
     __ ldr(ip, MemOperand(sp, 0));
     __ push(ip);
   } else {
     switch (top_of_stack_state_) {
       case NO_TOS_REGISTERS:
@@ skipping 247 matching lines @@
       break;
   }
   ASSERT(register_allocation_map_ == 0);  // Not yet implemented.
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM