fix doxygen brief in subzero header files

src/IceTargetLoweringX8664.h

Index: src/IceTargetLoweringX8664.h
diff --git a/src/IceTargetLoweringX8664.h b/src/IceTargetLoweringX8664.h
index b26db5962a27f8d3ecdd330ce95756c94b9b2d3b..6169dd27ac205e422055c4e24a4ba544c38cda99 100644
--- a/src/IceTargetLoweringX8664.h
+++ b/src/IceTargetLoweringX8664.h
@@ -8,7 +8,7 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file declares the TargetLoweringX8664 class, which implements the
+/// \brief Declares the TargetLoweringX8664 class, which implements the
 /// TargetLowering interface for the X86 64-bit architecture.
 ///
 //===----------------------------------------------------------------------===//