Fix include invocation

Index: obstack-wrapper.h
--- obstack-wrapper.h.orig
+++ obstack-wrapper.h
@@ -21,7 +21,7 @@
    also nullify object.  Since that breaks obstack_free (obstack_ptr, NULL), a
    new function obstack_destroy is added to support that functionaliy.  */
 
-#include <obstack.h>
+#include "obstack.h"
 
 /* Required definitions for obstack use.  */
 #define obstack_chunk_alloc malloc
