Add emitThumbSet to the arm target streamer.

This fixes the asm printer implementation and lets the parser be unaware of
what .thumb_set is.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207381 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCStreamer.h

@@ -121,6 +121,8 @@ public:
 
   virtual void AnnotateTLSDescriptorSequence(const MCSymbolRefExpr *SRE);
 
+  virtual void emitThumbSet(MCSymbol *Symbol, const MCExpr *Value);
+
   void finish() override;
 
   /// Callback used to implement the ldr= pseudo.