fix doxygen brief in subzero header files

src/IceInstVarIter.h

 //===- subzero/src/IceInstVarIter.h - Iterate over inst vars ----*- 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 a common pattern for iterating over the variables of an
+/// \brief Defines a common pattern for iterating over the variables of an
 /// instruction.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICEINSTVARITER_H
 #define SUBZERO_SRC_ICEINSTVARITER_H
 
 /// In Subzero, an Instr may have multiple Ice::Operands, and each Operand can
 /// have zero, one, or more Variables.
 ///
@@ skipping 142 matching lines @@
 #define IndexOfVarOperandInInst(Var) IsOnlyValidInFOREACH_VAR_IN_INST(I##Var)
 #define FOREACH_VAR_IN_INST_BREAK                                              \
   if (true) {                                                                  \
     Sz_Foreach_Break = 1;                                                      \
     continue;                                                                  \
   } else {                                                                     \
   }
 #undef OnlyValidIn_FOREACH_VAR_IN_INSTS
 
 #endif // SUBZERO_SRC_ICEINSTVARITER_H