Implement .weakref.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117911 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCNullStreamer.cpp b/lib/MC/MCNullStreamer.cpp
index b2db410..5f29b46 100644
--- a/lib/MC/MCNullStreamer.cpp
+++ b/lib/MC/MCNullStreamer.cpp
@@ -42,6 +42,7 @@
     virtual void EmitAssemblerFlag(MCAssemblerFlag Flag) {}
 
     virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {}
+    virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol){}
 
     virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute){}