fix doxygen brief in subzero header files

src/IceAssemblerX86BaseImpl.h

 //===- subzero/src/IceAssemblerX86BaseImpl.h - base x86 assembler -*- C++ -*-=//
 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // Modified by the Subzero authors.
 //
 //===----------------------------------------------------------------------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
-// This file implements the AssemblerX86Base template class, which is the base
-// Assembler class for X86 assemblers.
+/// \file
+/// \brief Implements the AssemblerX86Base template class, which is the base
+/// Assembler class for X86 assemblers.
 //
 //===----------------------------------------------------------------------===//
 
 #include "IceAssemblerX86Base.h"
 
 #include "IceCfg.h"
 #include "IceCfgNode.h"
 #include "IceOperand.h"
 
 namespace Ice {
@@ skipping 3417 matching lines @@
   (void)shifter;
   if (Ty == IceType_i16)
     emitOperandSizeOverride();
   emitRexB(Ty, operand.rm());
   emitUint8(isByteSizedArithType(Ty) ? 0xD2 : 0xD3);
   emitOperand(rm, operand);
 }
 
 } // end of namespace X86Internal
 } // end of namespace Ice