fix doxygen brief in subzero header files

src/IceTimerTree.cpp

 //===- subzero/src/IceTimerTree.cpp - Pass timer defs ---------------------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file defines the TimerTree class, which tracks flat and cumulative
+/// \brief Defines the TimerTree class, which tracks flat and cumulative
 /// execution time collection of call chains.
 ///
 //===----------------------------------------------------------------------===//
 
 #include "IceTimerTree.h"
 
 #include "IceDefs.h"
 
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wunused-parameter"
@@ skipping 279 matching lines @@
   dumpHelper(Str, FlatMap, TotalTime);
   Str << "Number of timer updates: " << StateChangeCount << "\n";
 }
 
 double TimerStack::timestamp() {
   // TODO: Implement in terms of std::chrono for C++11.
   return llvm::TimeRecord::getCurrentTime(false).getWallTime();
 }
 
 } // end of namespace Ice