Auto-sandboxing: Switch to automatic scratch register invalidation

lib/Target/X86/MCTargetDesc/X86MCNaClExpander.h

Index: lib/Target/X86/MCTargetDesc/X86MCNaClExpander.h
diff --git a/lib/Target/X86/MCTargetDesc/X86MCNaClExpander.h b/lib/Target/X86/MCTargetDesc/X86MCNaClExpander.h
index f084ac461c297ccbd522a091a737f7ad61ef6ec5..993fdd0b1a6ba081515a73a63c2697cf7a6bac9f 100644
--- a/lib/Target/X86/MCTargetDesc/X86MCNaClExpander.h
+++ b/lib/Target/X86/MCTargetDesc/X86MCNaClExpander.h
@@ -34,6 +34,9 @@ public:
 
   bool expandInst(const MCInst &Inst, MCStreamer &Out,
                   const MCSubtargetInfo &STI) override;
+protected:
+  bool isValidScratchRegister(unsigned Reg) const override;
+
 private:
   bool Guard = false; // recursion guard
   bool Is64Bit = false;