bind/java: fix build on NDK r16

Import <string.h> to provide a memcpy declaration.

Fixes golang/go#22766

Change-Id: I0762a1bb9d8d30bb1ae6f1a98648795ea57b0913
Reviewed-on: https://go-review.googlesource.com/79499
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

bind/java/seq_android.c.support

@@ -11,6 +11,7 @@
 #include <jni.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h>
 #include <unistd.h>
 #include <pthread.h>
 #include "seq.h"