Consolidate shift processing into utility function

src/IceTargetLoweringX86Base.h

Index: src/IceTargetLoweringX86Base.h
diff --git a/src/IceTargetLoweringX86Base.h b/src/IceTargetLoweringX86Base.h
index cdd07a6065d32da2ae55b2df013c6ede549bd84e..d96aa4fec040dee0cfd7ef2e58400238735c2587 100644
--- a/src/IceTargetLoweringX86Base.h
+++ b/src/IceTargetLoweringX86Base.h
@@ -715,6 +715,9 @@ 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