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/MCMachOStreamer.cpp b/lib/MC/MCMachOStreamer.cpp
index 2c0c97a..7d08d0e 100644
--- a/lib/MC/MCMachOStreamer.cpp
+++ b/lib/MC/MCMachOStreamer.cpp
@@ -34,9 +34,9 @@
   void EmitDataRegion(DataRegionData::KindTy Kind);
   void EmitDataRegionEnd();
 public:
-  MCMachOStreamer(MCContext &Context, MCAsmBackend &MAB,
-                  raw_ostream &OS, MCCodeEmitter *Emitter)
-    : MCObjectStreamer(Context, MAB, OS, Emitter) {}
+  MCMachOStreamer(MCContext &Context, MCAsmBackend &MAB, raw_ostream &OS,
+                  MCCodeEmitter *Emitter)
+      : MCObjectStreamer(SK_MachOStreamer, Context, MAB, OS, Emitter) {}
 
   /// @name MCStreamer Interface
   /// @{
@@ -87,6 +87,10 @@
   virtual void FinishImpl();
 
   /// @}
+
+  static bool classof(const MCStreamer *S) {
+    return S->getKind() == SK_MachOStreamer;
+  }
 };
 
 } // end anonymous namespace.