busybox: add 1.18.2 libbb fix

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/busybox/busybox-1.18.2/busybox-1.18.2-libbb.patch

@@ -0,0 +1,10 @@
+--- busybox-1.18.2/libbb/vfork_daemon_rexec.c
++++ busybox-1.18.2-libbb/libbb/vfork_daemon_rexec.c
+@@ -52,6 +52,7 @@ pid_t FAST_FUNC spawn(char **argv)
+ 	 * Interested party can wait on pid and learn exit code.
+ 	 * If 111 - then it (most probably) failed to exec */
+ 	if (failed) {
++		safe_waitpid(pid, NULL, 0); /* prevent zombie */
+ 		errno = failed;
+ 		return -1;
+ 	}