xenstore: talloc.h needs to include stdarg.h

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>

tools/xenstore/talloc.h

@@ -24,6 +24,7 @@
    License along with this library; If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <stdarg.h>
 #include <sys/types.h>
 
 #include "utils.h"