Fix build on arm and x64.

src/arm/register-allocator-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 78 matching lines @@
   // during execution.
   Use(sp);  // Stack pointer.
   Use(fp);  // Frame pointer (caller's frame pointer on entry).
   Use(cp);  // Context context (callee's context on entry).
   Use(pc);  // Program counter.
 }
 
 
 Result RegisterAllocator::AllocateByteRegisterWithoutSpilling() {
   UNIMPLEMENTED();
-  Result invalid(cgen_);
-  return invalid;
+  return Result();
 }
 
 
 } }  // namespace v8::internal