fix doxygen brief in subzero header files

src/IceRegList.h

 //===- subzero/src/IceRegList.h - Register list macro defs  -----*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
-// This file defines the REGLIST*() macros used in the IceInst*.def files.
-//
+/// \file
+/// \brief Defines the REGLIST*() macros used in the IceInst*.def files.
+///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICEINSTREGLIST_H
 #define SUBZERO_SRC_ICEINSTREGLIST_H
 
 // REGLISTn is a family of macros that we use to define register aliasing.  "n"
 // indicates how many register aliases are being provided to the macro.  It
 // assumes the parameters are register names declared in the "ns"
 // namespace/class, but with the common "Reg_" prefix removed for brevity.
 #define REGLIST1(ns, r0)                                                       \
   { ns::Reg_##r0 }
 #define REGLIST2(ns, r0, r1)                                                   \
   { ns::Reg_##r0, ns::Reg_##r1 }
 #define REGLIST3(ns, r0, r1, r2)                                               \
   { ns::Reg_##r0, ns::Reg_##r1, ns::Reg_##r2 }
 #define REGLIST4(ns, r0, r1, r2, r3)                                           \
   { ns::Reg_##r0, ns::Reg_##r1, ns::Reg_##r2, ns::Reg_##r3 }
 #define REGLIST6(ns, r0, r1, r2, r3, r4, r5)                                   \
   {                                                                            \
     ns::Reg_##r0, ns::Reg_##r1, ns::Reg_##r2, ns::Reg_##r3, ns::Reg_##r4,      \
         ns::Reg_##r5                                                           \
   }
 
 #endif // SUBZERO_SRC_ICEINSTREGLIST_H