Give the MCStreamer class hierarchy LLVM RTTI facilities for use with
isa<> and dyn_cast<>. In several places, code is already hacking around
the absence of this, and there seem to be several interfaces that might
be lifted and/or devirtualized using this.

This change was based on a discussion with Jim Grosbach about how best
to handle testing for specific MCStreamer subclasses. He said that this
was the correct end state, and everything else was too hacky so
I decided to just make it so.

No functionality should be changed here, this is just threading the kind
through all the constructors and setting up the classof overloads.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174113 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCAsmStreamer.cpp b/lib/MC/MCAsmStreamer.cpp
index 7191947..71be1a9 100644
--- a/lib/MC/MCAsmStreamer.cpp
+++ b/lib/MC/MCAsmStreamer.cpp
@@ -71,7 +71,7 @@
                 MCInstPrinter *printer, MCCodeEmitter *emitter,
                 MCAsmBackend *asmbackend,
                 bool showInst)
-    : MCStreamer(Context), OS(os), MAI(Context.getAsmInfo()),
+    : MCStreamer(SK_AsmStreamer, Context), OS(os), MAI(Context.getAsmInfo()),
       InstPrinter(printer), Emitter(emitter), AsmBackend(asmbackend),
       CommentStream(CommentToEmit), IsVerboseAsm(isVerboseAsm),
       ShowInst(showInst), UseLoc(useLoc), UseCFI(useCFI),
@@ -277,6 +277,10 @@
   virtual void FinishImpl();
 
   /// @}
+
+  static bool classof(const MCStreamer *S) {
+    return S->getKind() == SK_NullStreamer;
+  }
 };
 
 } // end anonymous namespace.