[MC] Implement the COFF directives in MCNullStreamer.

This fixes -filetype=null errors introduced in r296403.

llvm-svn: 296410

Author: Dan Gohman

llvm/lib/MC/MCNullStreamer.cpp

@@ -34,6 +34,10 @@ namespace {
     void EmitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
                       uint64_t Size = 0, unsigned ByteAlignment = 0) override {}
     void EmitGPRel32Value(const MCExpr *Value) override {}
+    void BeginCOFFSymbolDef(const MCSymbol *Symbol) override {}
+    void EmitCOFFSymbolStorageClass(int StorageClass) override {}
+    void EmitCOFFSymbolType(int Type) override {}
+    void EndCOFFSymbolDef() override {}
   };
 
 }