fix doxygen brief in subzero header files

src/IceUtils.h

 //===- subzero/src/IceUtils.h - Utility 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 some utility functions.
+/// \brief Defines some utility functions.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICEUTILS_H
 #define SUBZERO_SRC_ICEUTILS_H
 
 #include <climits>
 #include <cmath> // std::signbit()
 
 namespace Ice {
@@ skipping 101 matching lines @@
   template <typename T> static bool isPositiveZero(T Val) {
     static_assert(std::is_floating_point<T>::value,
                   "Input type must be floating point");
     return Val == 0 && !std::signbit(Val);
   }
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEUTILS_H