fix doxygen brief in subzero header files

src/IceCfg.h

 //===- subzero/src/IceCfg.h - Control flow graph ----------------*- 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 declares the Cfg class, which represents the control flow graph
-/// and the overall per-function compilation context.
+/// \brief Declares the Cfg class, which represents the control flow graph and
+/// the overall per-function compilation context.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICECFG_H
 #define SUBZERO_SRC_ICECFG_H
 
 #include "IceAssembler.h"
 #include "IceClFlags.h"
 #include "IceDefs.h"
 #include "IceGlobalContext.h"
@@ skipping 286 matching lines @@
 
 public:
   static void TlsInit() { ICE_TLS_INIT_FIELD(CurrentCfg); }
 };
 
 template <> Variable *Cfg::makeVariable<Variable>(Type Ty);
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICECFG_H