Consolidate shift processing into utility function

src/IceTargetLoweringX86Base.h

Index: src/IceTargetLoweringX86Base.h
diff --git a/src/IceTargetLoweringX86Base.h b/src/IceTargetLoweringX86Base.h
index 4ce2ec188408cd259b64eb5cb5d7db1448cddd0c..6d0aa0fccd67761f3ae6d12351d9cd10442af87f 100644
--- a/src/IceTargetLoweringX86Base.h
+++ b/src/IceTargetLoweringX86Base.h
@@ -713,6 +713,9 @@ private:
     (static_cast<Machine *>(this)->*Method)(std::forward<Args>(args)...);
   }
 
+  void lowerShift64(InstArithmetic::OpKind Op, Operand *Src0Lo, Operand *Src0Hi,
+                    Operand *Src1Lo, Variable *DestLo, Variable *DestHi);
+
   BoolFolding FoldingInfo;
 };
 } // end of namespace X86Internal