Fix compile error on NDK r16

Author: John-He-928

android/jni/com_tencent_wcdb_repair_DBDumpUtil.cpp

@@ -25,6 +25,7 @@
 #include <sqlite3.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include "JNIHelp.h"
 #include "Logger.h"

android/jni/com_tencent_wcdb_repair_RepairKit.cpp

@@ -25,6 +25,7 @@
 #include <repair/SQLiteRepairKit.h>
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
 
 static int g_error_result = 0;
 static char g_error_msg[2048] = {0};

backup/mm_backup.c

@@ -25,6 +25,7 @@
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <sys/stat.h>
 
 #include <openssl/rc4.h>