fix doxygen brief in subzero header files

src/IceAssembler.h

Index: src/IceAssembler.h
diff --git a/src/IceAssembler.h b/src/IceAssembler.h
index 599a0a0d4bb1db807de022a30e0d7571052891b9..d80e3d26e9b4f4f1b8d2a09e06e4539efb7993b7 100644
--- a/src/IceAssembler.h
+++ b/src/IceAssembler.h
@@ -15,9 +15,11 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file declares the Assembler base class. Instructions are assembled by
-/// architecture-specific assemblers that derive from this base class. This base
-/// class manages buffers and fixups for emitting code, etc.
+/// \brief Declares the Assembler base class.
+///
+/// Instructions are assembled by architecture-specific assemblers that derive
+/// from this base class. This base class manages buffers and fixups for
+/// emitting code, etc.
 ///
 //===----------------------------------------------------------------------===//