fix doxygen brief in subzero header files

src/IceThreading.h

 //===- subzero/src/IceThreading.h - Threading functions ---------*- 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 threading-related functions.
+/// \brief Declares threading-related functions.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICETHREADING_H
 #define SUBZERO_SRC_ICETHREADING_H
 
 #include "IceDefs.h"
 
 #include <condition_variable>
 #include <mutex>
@@ skipping 168 matching lines @@
   const uint32_t Sequence;
   const ItemKind Kind;
   std::unique_ptr<VariableDeclarationList> GlobalInits;
   std::unique_ptr<Assembler> Function;
   std::unique_ptr<Cfg> RawFunc;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETHREADING_H