Add include to silence compiler warning when compiling clone.c for AVR32

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>

libc/sysdeps/linux/avr32/clone.c

@@ -5,6 +5,7 @@
  * Public License.  See the file "COPYING.LIB" in the main directory of this
  * archive for more details.
  */
+#include <sched.h>
 #include <errno.h>
 #include <sys/syscall.h>
 #include <unistd.h>