Enables llvm dyn_cast for Assemblers.

src/IceAssemblerX8632.h

Index: src/IceAssemblerX8632.h
diff --git a/src/IceAssemblerX8632.h b/src/IceAssemblerX8632.h
index 132e72d610267b374ceb894350e20a7e43713ac7..8b13fc62ead65acadd912b65a5873b9eb64ff46c 100644
--- a/src/IceAssemblerX8632.h
+++ b/src/IceAssemblerX8632.h
@@ -337,7 +337,8 @@ class AssemblerX8632 : public Assembler {
   AssemblerX8632 &operator=(const AssemblerX8632 &) = delete;
 
 public:
-  explicit AssemblerX8632(bool use_far_branches = false) : Assembler() {
+  explicit AssemblerX8632(bool use_far_branches = false)
+      : Assembler(Asm_X8632) {
     // This mode is only needed and implemented for MIPS and ARM.
     assert(!use_far_branches);
     (void)use_far_branches;
@@ -377,6 +378,10 @@ public:
     return Kind == llvm::ELF::R_386_PC32;
   }
 
+  static bool classof(const Assembler *Asm) {
+    return Asm->getKind() == Asm_X8632;
+  }
+
   // Operations to emit GPR instructions (and dispatch on operand type).
   typedef void (AssemblerX8632::*TypedEmitGPR)(Type, GPRRegister);
   typedef void (AssemblerX8632::*TypedEmitAddr)(Type, const Address &);