talloc_vasprintf() has a va_list type parameter, so this type needs to
be defined (independent of the particular libc implementation).
Fixes: 63b6419d2a ("tools/xenstore: split out rest of live update control code")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>