fix doxygen brief in subzero header files

src/IceInst.h

Index: src/IceInst.h
diff --git a/src/IceInst.h b/src/IceInst.h
index a04584e2a6f5862bc2adc1842c28884a1a5160e4..f9265f6920ebc68c7fa7d097ec0165359454ab73 100644
--- a/src/IceInst.h
+++ b/src/IceInst.h
@@ -8,9 +8,10 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file declares the Inst class and its target-independent
-/// subclasses, which represent the high-level Vanilla ICE instructions
-/// and map roughly 1:1 to LLVM instructions.
+/// \brief Declares the Inst class and its target-independent subclasses.
+///
+/// These represent the high-level Vanilla ICE instructions and map roughly 1:1
+/// to LLVM instructions.
 ///
 //===----------------------------------------------------------------------===//