Workaround GCC 4.0.1 on the Darwin builds.

* src/misc/bitvect.hh: Remove SPOT_API from class forward declarations.
* src/ltlast/nfa.hh: Likewise.

src/ltlast/nfa.hh

 // -*- coding: utf-8 -*-
-// Copyright (C) 2008, 2010, 2013 Laboratoire de Recherche et
+// Copyright (C) 2008, 2010, 2013, 2014 Laboratoire de Recherche et
 // Développement de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
@@ -34,7 +34,7 @@ namespace spot
   namespace ltl
   {
     /// Forward declaration. See below.
-    class SPOT_API succ_iterator;
+    class succ_iterator;
     /// Forward declaration. NFA's labels are reprensented by nodes
     /// which are defined in formula_tree.hh, included in nfa.cc.
     namespace formula_tree

src/misc/bitvect.hh

 // -*- coding: utf-8 -*-
-// Copyright (C) 2013 Laboratoire de Recherche et Développement
+// Copyright (C) 2013, 2014 Laboratoire de Recherche et Développement
 // de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
@@ -31,8 +31,8 @@ namespace spot
   /// \addtogroup misc_tools
   /// @{
 
-  class SPOT_API bitvect;
-  class SPOT_API bitvect_array;
+  class bitvect;
+  class bitvect_array;
 
   ///\brief Allocate a bit-vector of \a bitcount bits.
   ///