fix doxygen brief in subzero header files

src/IceInstX86Base.h

Index: src/IceInstX86Base.h
diff --git a/src/IceInstX86Base.h b/src/IceInstX86Base.h
index 6e9d7bad4a27d01ddf27dd8f8d646949ad53a272..9c9ebf716dddcf0eba409cdda5fcff4c709b3ac6 100644
--- a/src/IceInstX86Base.h
+++ b/src/IceInstX86Base.h
@@ -8,10 +8,11 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file defines the InstX86Base template class, as well as the generic X86
-/// Instruction class hierarchy. Only X86 instructions common across all/most
-/// X86 targets should be defined here, with target-specific instructions
-/// declared in the target's traits.
+/// \brief This file defines the InstX86Base template class, as well as the
+/// generic X86 Instruction class hierarchy.
+///
+/// Only X86 instructions common across all/most X86 targets should be defined
+/// here, with target-specific instructions declared in the target's traits.
 ///
 //===----------------------------------------------------------------------===//