fix doxygen brief in subzero header files

src/IceRNG.h

 //===- subzero/src/IceRNG.h - Random number generator -----------*- 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 a random number generator.
+/// \brief Declares a random number generator.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICERNG_H
 #define SUBZERO_SRC_ICERNG_H
 
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Compiler.h"
 #include "IceDefs.h"
 
@@ skipping 54 matching lines @@
 /// at cppreference.com.
 template <class RandomIt, class RandomFunc>
 void RandomShuffle(RandomIt First, RandomIt Last, RandomFunc &&RNG) {
   for (auto i = Last - First - 1; i > 0; --i)
     std::swap(First[i], First[RNG(i + 1)]);
 }
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICERNG_H