fix doxygen brief in subzero header files

src/IceTargetLoweringX86RegClass.h

 //===- subzero/src/IceTargetLoweringX86RegClass.h - x86 reg class -*- 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 the X86 register class extensions.
+/// \brief Declares the X86 register class extensions.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICETARGETLOWERINGX86REGCLASS_H
 #define SUBZERO_SRC_ICETARGETLOWERINGX86REGCLASS_H
 
 #include "IceOperand.h" // RC_Target
 
 namespace Ice {
 namespace X86Internal {
 
 // Extend enum RegClass with x86-specific register classes.
 enum RegClassX86 : uint8_t {
   RCX86_Is64To8 = RC_Target, // 64-bit GPR trivially truncable to 8-bit
   RCX86_Is32To8,             // 32-bit GPR trivially truncable to 8-bit
   RCX86_Is16To8,             // 16-bit GPR trivially truncable to 8-bit
   RCX86_IsTrunc8Rcvr,        // 8-bit GPR that can receive a trunc operation
   RCX86_IsAhRcvr,            // 8-bit GPR that can be a mov dest from %ah
   RCX86_NUM
 };
 
 } // end of namespace X86Internal
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETARGETLOWERINGX86REGCLASS_H