Add hybrid assembler concept to ARM assembler.

src/IceFixups.h

 //===- subzero/src/IceFixups.h - Assembler fixup kinds ----------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 27 matching lines @@
   void set_kind(FixupKind Kind) { kind_ = Kind; }
 
   RelocOffsetT offset() const;
   IceString symbol(const GlobalContext *Ctx) const;
 
   static const Constant *NullSymbol;
   bool isNullSymbol() const { return value_ == NullSymbol; }
 
   void set_value(const Constant *Value) { value_ = Value; }
 
-  void emit(GlobalContext *Ctx, RelocOffsetT OverrideOffset) const;
+  // Emits fixup, then returns the number of bytes to skip.
+  virtual size_t emit(GlobalContext *Ctx, RelocOffsetT OverrideOffset,
+                      bool IsPCRel) const;
 
 private:
   intptr_t position_ = 0;
   FixupKind kind_ = 0;
   const Constant *value_ = nullptr;
 };
 
 using FixupList = std::vector<AssemblerFixup>;
 using FixupRefList = std::vector<AssemblerFixup *>;
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEFIXUPS_H