add emacs magic comment

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@42294 138bc75d-0d04-0410-961f-82ee72b054a4

gcc/unwind.inc

-/* Exception handling and frame unwind runtime interface routines.
+/* Exception handling and frame unwind runtime interface routines. -*- C -*-
    Copyright (C) 2001 Free Software Foundation, Inc.
 
    This file is part of GNU CC.