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

tools/lto/LTOModule.cpp

@@ -733,7 +733,8 @@ namespace {
       return Symbols.end();
     }
 
-    RecordStreamer(MCContext &Context) : MCStreamer(Context) {}
+    RecordStreamer(MCContext &Context)
+        : MCStreamer(SK_RecordStreamer, Context) {}
 
     virtual void EmitInstruction(const MCInst &Inst) {
       // Scan for values.
@@ -804,6 +805,10 @@ namespace {
                                           const MCSymbol *Label,
                                           unsigned PointerSize) {}
     virtual void FinishImpl() {}
+
+    static bool classof(const MCStreamer *S) {
+      return S->getKind == SK_RecordStreamer;
+    }
   };
 } // end anonymous namespace