fix doxygen brief in subzero header files

src/IceTargetLoweringX8664.cpp

Index: src/IceTargetLoweringX8664.cpp
diff --git a/src/IceTargetLoweringX8664.cpp b/src/IceTargetLoweringX8664.cpp
index c1692425224d1bb6013395cb25c1e2459c9a64cd..ceaaede2e46e5b4d4dcc172e1b03300913fe83e5 100644
--- a/src/IceTargetLoweringX8664.cpp
+++ b/src/IceTargetLoweringX8664.cpp
@@ -8,7 +8,7 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file implements the TargetLoweringX8664 class, which consists almost
+/// \brief Implements the TargetLoweringX8664 class, which consists almost
 /// entirely of the lowering sequence for each high-level instruction.
 ///
 //===----------------------------------------------------------------------===//