fix doxygen brief in subzero header files

src/IceTargetLoweringX8632.cpp

Index: src/IceTargetLoweringX8632.cpp
diff --git a/src/IceTargetLoweringX8632.cpp b/src/IceTargetLoweringX8632.cpp
index 198273b8c6d704158aa74618e825c4945fbcfa37..00196933d65155864da4d052e6e88591b32e570c 100644
--- a/src/IceTargetLoweringX8632.cpp
+++ b/src/IceTargetLoweringX8632.cpp
@@ -8,7 +8,7 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file implements the TargetLoweringX8632 class, which consists almost
+/// \brief Implements the TargetLoweringX8632 class, which consists almost
 /// entirely of the lowering sequence for each high-level instruction.
 ///
 //===----------------------------------------------------------------------===//