fix doxygen brief in subzero header files

src/IceInstX86BaseImpl.h

 //===- subzero/src/IceInstX86BaseImpl.h - Generic X86 instructions -*- C++ -*=//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file implements the InstX86Base class and its descendants.
+/// \brief Implements the InstX86Base class and its descendants.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICEINSTX86BASEIMPL_H
 #define SUBZERO_SRC_ICEINSTX86BASEIMPL_H
 
 #include "IceInstX86Base.h"
 
 #include "IceAssemblerX86Base.h"
 #include "IceCfg.h"
@@ skipping 3164 matching lines @@
     return;
   Ostream &Str = Func->getContext()->getStrDump();
   Str << "IACA_END";
 }
 
 } // end of namespace X86Internal
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEINSTX86BASEIMPL_H