Merge lowerCall and lowerRet between x86 and x64

src/IceTargetLoweringX8664.h

 //===- subzero/src/IceTargetLoweringX8664.h - lowering for x86-64 -*- C++ -*-=//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 42 matching lines @@
 
 protected:
   void _add_sp(Operand *Adjustment);
   void _mov_sp(Operand *NewValue);
   void _push_rbp();
   Traits::X86OperandMem *_sandbox_mem_reference(X86OperandMem *Mem);
   void _sub_sp(Operand *Adjustment);
 
   void initSandbox();
   void lowerIndirectJump(Variable *JumpTarget);
-  void lowerCall(const InstCall *Instr) override;
-  void lowerArguments() override;
-  void lowerRet(const InstRet *Inst) override;
+  Inst *emitCallToTarget(Operand *CallTarget, Variable *ReturnReg) override;
+  Variable *moveReturnValueToRegister(Operand *Value,
+                                      const Type ReturnType) override;
   void addProlog(CfgNode *Node) override;
   void addEpilog(CfgNode *Node) override;
 
 private:
   ENABLE_MAKE_UNIQUE;
   friend class X8664::TargetX86Base<X8664::Traits>;
 
   explicit TargetX8664(Cfg *Func)
       : ::Ice::X8664::TargetX86Base<X8664::Traits>(Func) {}
 
@@ skipping 45 matching lines @@
 private:
   ENABLE_MAKE_UNIQUE;
 
   explicit TargetHeaderX8664(GlobalContext *Ctx) : TargetHeaderLowering(Ctx) {}
 };
 
 } // end of namespace X8664
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETARGETLOWERINGX8664_H