Subzero: Change the way bitcast stack slot lowering is handled.

src/IceOperand.cpp

Index: src/IceOperand.cpp
diff --git a/src/IceOperand.cpp b/src/IceOperand.cpp
index 1f232dd61a39b2a1332b6ee5eaced5b11271d317..e4aaf2475671163390b6b86e03d292df27e44091 100644
--- a/src/IceOperand.cpp
+++ b/src/IceOperand.cpp
@@ -189,7 +189,9 @@ IceString Variable::getName() const {
 }
 
 Variable Variable::asType(Type Ty) {
-  Variable V(Ty, DefNode, Number, Name);
+  // Note: This returns a Variable, even if the "this" object is a
+  // subclass of Variable.
+  Variable V(kVariable, Ty, DefNode, Number, Name);
   V.RegNum = RegNum;
   V.StackOffset = StackOffset;
   return V;