fix doxygen brief in subzero header files

src/IceTargetLoweringX86BaseImpl.h

Index: src/IceTargetLoweringX86BaseImpl.h
diff --git a/src/IceTargetLoweringX86BaseImpl.h b/src/IceTargetLoweringX86BaseImpl.h
index f3246ef4ab4d06fbad8673d4a5824c2b12e8d611..1818f023d07449cdc6e85c09cb6facb68857fa1b 100644
--- a/src/IceTargetLoweringX86BaseImpl.h
+++ b/src/IceTargetLoweringX86BaseImpl.h
@@ -8,7 +8,7 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file implements the TargetLoweringX86Base class, which consists almost
+/// \brief Implements the TargetLoweringX86Base class, which consists almost
 /// entirely of the lowering sequence for each high-level instruction.
 ///
 //===----------------------------------------------------------------------===//