Make the use of xmm0 as double scratch register explicit in ia32 and x64.

src/x64/lithium-codegen-x64.h

 // Copyright 2012 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 148 matching lines @@
   bool is_aborted() const { return status_ == ABORTED; }
 
   StrictModeFlag strict_mode_flag() const {
     return info()->is_classic_mode() ? kNonStrictMode : kStrictMode;
   }
 
   LPlatformChunk* chunk() const { return chunk_; }
   Scope* scope() const { return scope_; }
   HGraph* graph() const { return chunk()->graph(); }
 
+  XMMRegister double_scratch0() const { return xmm0; }
+
   int GetNextEmittedBlock() const;
 
   void EmitClassOfTest(Label* if_true,
                        Label* if_false,
                        Handle<String> class_name,
                        Register input,
                        Register temporary,
                        Register scratch);
 
   int GetStackSlotCount() const { return chunk()->spill_slot_count(); }
@@ skipping 262 matching lines @@
   Label entry_;
   Label exit_;
   Label done_;
   Label* external_exit_;
   int instruction_index_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_LITHIUM_CODEGEN_X64_H_