Enables llvm dyn_cast for Assemblers.

src/IceAssemblerARM32.h

Index: src/IceAssemblerARM32.h
diff --git a/src/IceAssemblerARM32.h b/src/IceAssemblerARM32.h
index a0322041ba60d0ea418acc5db78a7702fd1a1a85..f67b63041724a3b2cab7bb0ec4801e4002aeb7c8 100644
--- a/src/IceAssemblerARM32.h
+++ b/src/IceAssemblerARM32.h
@@ -34,7 +34,8 @@ class AssemblerARM32 : public Assembler {
   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;
@@ -68,6 +69,10 @@ public:
     (void)Kind;
     llvm_unreachable("Not yet implemented.");
   }
+
+  static bool classof(const Assembler *Asm) {
+    return Asm->getKind() == Asm_ARM32;
+  }
 };
 
 } // end of namespace ARM32