fix doxygen brief in subzero header files

src/IceFixups.cpp

 //===- subzero/src/IceFixups.cpp - Implementation of Assembler Fixups -----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file implements the AssemblerFixup class, a very basic
-/// target-independent representation of a fixup or relocation.
+/// \brief Implements the AssemblerFixup class, a very basic target-independent
+/// representation of a fixup or relocation.
 ///
 //===----------------------------------------------------------------------===//
 
 #include "IceFixups.h"
 
 #include "IceOperand.h"
 
 namespace Ice {
 
 const Constant *AssemblerFixup::NullSymbol = nullptr;
@@ skipping 47 matching lines @@
   Str << "\n";
   return FixupSize;
 }
 
 size_t AssemblerTextFixup::emit(GlobalContext *Ctx, const Assembler &) const {
   Ctx->getStrEmit() << Message << "\n";
   return NumBytes;
 }
 
 } // end of namespace Ice