Enables llvm dyn_cast for Assemblers.

src/IceAssemblerARM32.h

 //===- subzero/src/IceAssemblerARM32.h - Assembler for ARM32 ----*- C++ -*-===//
 //
 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // Modified by the Subzero authors.
 //
 //===----------------------------------------------------------------------===//
 //
@@ skipping 16 matching lines @@
 #include "IceFixups.h"
 
 namespace Ice {
 namespace ARM32 {
 
 class AssemblerARM32 : public Assembler {
   AssemblerARM32(const AssemblerARM32 &) = delete;
   AssemblerARM32 &operator=(const AssemblerARM32 &) = delete;
 
 public:
-  explicit AssemblerARM32(bool use_far_branches = false) : Assembler() {
+  explicit AssemblerARM32(bool use_far_branches = false)
+      : Assembler(Asm_ARM32) {
     // This mode is only needed and implemented for MIPS and ARM.
     assert(!use_far_branches);
     (void)use_far_branches;
   }
   ~AssemblerARM32() override = default;
 
   void alignFunction() override { llvm_unreachable("Not yet implemented."); }
 
   SizeT getBundleAlignLog2Bytes() const override { return 4; }
 
@@ skipping 13 matching lines @@
 
   void bindCfgNodeLabel(SizeT NodeNumber) override {
     (void)NodeNumber;
     llvm_unreachable("Not yet implemented.");
   }
 
   bool fixupIsPCRel(FixupKind Kind) const override {
     (void)Kind;
     llvm_unreachable("Not yet implemented.");
   }
+
+  static bool classof(const Assembler *Asm) {
+    return Asm->getKind() == Asm_ARM32;
+  }
 };
 
 } // end of namespace ARM32
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEASSEMBLERARM32_H