make the NullStreamer set the section on a label when emitted so that isDefined() works.

llvm-svn: 98100
diff --git a/llvm/lib/MC/MCNullStreamer.cpp b/llvm/lib/MC/MCNullStreamer.cpp
index ab61799..5f0c64a 100644
--- a/llvm/lib/MC/MCNullStreamer.cpp
+++ b/llvm/lib/MC/MCNullStreamer.cpp
@@ -29,7 +29,11 @@
       CurSection = Section;
     }
 
-    virtual void EmitLabel(MCSymbol *Symbol) {}
+    virtual void EmitLabel(MCSymbol *Symbol) {
+      assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
+      assert(CurSection && "Cannot emit before setting section!");
+      Symbol->setSection(*CurSection);
+    }
 
     virtual void EmitAssemblerFlag(MCAssemblerFlag Flag) {}