introduce async_callback_ftype

This introduces async_callback_ftype.  This is needed for
make-target-delegates to work properly, as it doesn't implement a real
parser.  I think it's also an ok cleanup in its own right.

2014-01-15  Tom Tromey  <tromey@redhat.com>

	* target.h (async_callback_ftype): New typedef.
	(struct target_ops) <to_async>: Use it.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2014-01-15  Tom Tromey  <tromey@redhat.com>
+
+	* target.h (async_callback_ftype): New typedef.
+	(struct target_ops) <to_async>: Use it.
+
 2014-01-15  Joel Brobecker  <brobecker@adacore.com>
 
 	* python/py-value.c (get_field_type): Remove unnecessary curly

gdb/target.h

@@ -345,6 +345,11 @@ extern ULONGEST get_target_memory_unsigned (struct target_ops *ops,
 
 struct thread_info;		/* fwd decl for parameter list below: */
 
+/* The type of the callback to the to_async method.  */
+
+typedef void async_callback_ftype (enum inferior_event_type event_type,
+				   void *context);
+
 struct target_ops
   {
     struct target_ops *beneath;	/* To the target under this one.  */
@@ -486,7 +491,7 @@ struct target_ops
     /* ASYNC target controls */
     int (*to_can_async_p) (void);
     int (*to_is_async_p) (void);
-    void (*to_async) (void (*) (enum inferior_event_type, void *), void *);
+    void (*to_async) (async_callback_ftype *, void *);
     int (*to_supports_non_stop) (void);
     /* find_memory_regions support method for gcore */
     int (*to_find_memory_regions) (find_memory_region_ftype func, void *data);