Subzero: Clean up some uses of *_cast<>.

src/IceInstARM32.h

 //===- subzero/src/IceInstARM32.h - ARM32 machine instructions --*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 330 matching lines @@
 /// range.
 class StackVariable final : public Variable {
   StackVariable() = delete;
   StackVariable(const StackVariable &) = delete;
   StackVariable &operator=(const StackVariable &) = delete;
 
 public:
   static StackVariable *create(Cfg *Func, Type Ty, SizeT Index) {
     return new (Func->allocate<StackVariable>()) StackVariable(Ty, Index);
   }
-  const static OperandKind StackVariableKind =
+  constexpr static auto StackVariableKind =
       static_cast<OperandKind>(kVariable_Target);
   static bool classof(const Operand *Operand) {
     return Operand->getKind() == StackVariableKind;
   }
   void setBaseRegNum(int32_t RegNum) { BaseRegNum = RegNum; }
   int32_t getBaseRegNum() const override { return BaseRegNum; }
   // Inherit dump() and emit() from Variable.
 
 private:
   StackVariable(Type Ty, SizeT Index)
@@ skipping 1077 matching lines @@
 // violations and link errors.
 
 template <> void InstARM32Ldr::emit(const Cfg *Func) const;
 template <> void InstARM32Movw::emit(const Cfg *Func) const;
 template <> void InstARM32Movt::emit(const Cfg *Func) const;
 
 } // end of namespace ARM32
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEINSTARM32_H