fix doxygen brief in subzero header files

src/IceClFlags.cpp

Index: src/IceClFlags.cpp
diff --git a/src/IceClFlags.cpp b/src/IceClFlags.cpp
index 6966210e4dce3ddf84c761a90eaa09b23ceabe8e..4ecb0251a43d80add3ac7bc69acdd3d97cd2ab1f 100644
--- a/src/IceClFlags.cpp
+++ b/src/IceClFlags.cpp
@@ -8,9 +8,10 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file defines commandline flags parsing. This currently relies on
-/// llvm::cl to parse. In the future, the minimal build can have a simpler
-/// parser.
+/// \brief Defines commandline flags parsing.
+///
+/// This currently relies on llvm::cl to parse. In the future, the minimal
+/// build can have a simpler parser.
 ///
 //===----------------------------------------------------------------------===//