tests: process-list add stdlib include

Signed-off-by: Jan Friesse <jfriesse@redhat.com>

qdevices/test-process-list.c

@@ -40,6 +40,7 @@
 #include <string.h>
 #include <poll.h>
 #include <signal.h>
+#include <stdlib.h>
 #include <limits.h>
 #include <unistd.h>