fix doxygen brief in subzero header files

src/IceBuildDefs.h

 //===- subzero/src/IceBuildDefs.h - Translator build defines ----*- 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 defines constexpr functions to query various #define values.
+/// \brief Defines constexpr functions to query various #define values.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICEBUILDDEFS_H
 #define SUBZERO_SRC_ICEBUILDDEFS_H
 
 namespace Ice {
 namespace BuildDefs {
 
 // The ALLOW_* etc. symbols must be #defined to zero or non-zero.
@@ skipping 19 matching lines @@
   return true;
 #else  // !ALLOW_EXTRA_VALIDATION
   return false;
 #endif // !ALLOW_EXTRA_VALIDATION
 }
 
 } // end of namespace BuildDefs
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEBUILDDEFS_H