fix building of cpu-test by including required header

Originally committed as revision 25917 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/cpu.c

@@ -16,6 +16,8 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include <stdio.h>
+
 #include "cpu.h"
 #include "config.h"