- env

 cat /etc/*release
Oracle Linux Server release 7.1
NAME="Oracle Linux Server"
VERSION="7.1"
ID="ol"
VERSION_ID="7.1"
PRETTY_NAME="Oracle Linux Server 7.1"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:oracle:linux:7:1"
HOME_URL="https://linux.oracle.com/"
BUG_REPORT_URL="https://bugzilla.oracle.com/"

ORACLE_BUGZILLA_PRODUCT="Oracle Linux 7"
ORACLE_BUGZILLA_PRODUCT_VERSION=7.1
ORACLE_SUPPORT_PRODUCT="Oracle Linux"
ORACLE_SUPPORT_PRODUCT_VERSION=7.1
Red Hat Enterprise Linux Server release 7.1 (Maipo)
Oracle Linux Server release 7.1

- binary tarball

cat docs/INFO_SRC
commit: a5b2e523c881ab8c68fd0adb478a6232dd69e522
date: 2019-06-25 11:50:40 +0200
build-date: 2019-06-25 12:24:04 +0200
short: a5b2e52
branch: mysql-8.0.17-release

MySQL source 8.0.17

rm -rf 96281/
bin/mysqld --initialize-insecure --basedir=$PWD --datadir=$PWD/96281 --log-error-verbosity=3
bin/mysqld --no-defaults --basedir=$PWD --datadir=$PWD/96281 --core-file --socket=/tmp/mysql_ushastry.sock  --port=3333 --log-error=$PWD/96281/log.err --mysqlx-port=33330 --mysqlx-socket=/tmp/mysql_x_ushastry.sock --log-error-verbosity=3  --secure-file-priv=/tmp/ 2>&1 &

bin/mysql -uroot -S /tmp/mysql_ushastry.sock
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 7
Server version: 8.0.17 MySQL Community Server - GPL

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> INSTALL PLUGIN clone SONAME 'mysql_clone.so';
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT PLUGIN_NAME, PLUGIN_STATUS
    ->        FROM INFORMATION_SCHEMA.PLUGINS
    ->        WHERE PLUGIN_NAME LIKE 'clone';
+-------------+---------------+
| PLUGIN_NAME | PLUGIN_STATUS |
+-------------+---------------+
| clone       | ACTIVE        |
+-------------+---------------+
1 row in set (0.01 sec)

mysql> system cat docs/INFO_SRC
commit: a5b2e523c881ab8c68fd0adb478a6232dd69e522
date: 2019-06-25 11:50:40 +0200
build-date: 2019-06-25 12:24:04 +0200
short: a5b2e52
branch: mysql-8.0.17-release

MySQL source 8.0.17

mysql>

- with my.cnf provided by Simon


rm -rf 96281/
bin/mysqld --defaults-file=./my.cnf --initialize-insecure --basedir=$PWD --datadir=$PWD/96281 --log-error-verbosity=3
bin/mysqld --defaults-file=./my.cnf --basedir=$PWD --datadir=$PWD/96281 --core-file --socket=/tmp/mysql_ushastry.sock  --port=3333 --mysqlx-port=33330 --mysqlx-socket=/tmp/mysql_x_ushastry.sock --log-error-verbosity=3  --secure-file-priv=/tmp/ 2>&1 &

 bin/mysql -uroot -S /tmp/mysql_ushastry.sock
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 7
Server version: 8.0.17 MySQL Community Server - GPL

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> set global read_only = 0;
Query OK, 0 rows affected (0.00 sec)

mysql> INSTALL PLUGIN clone SONAME 'mysql_clone.so';
ERROR 1123 (HY000): Can't initialize function 'clone'; Plugin initialization function failed.
mysql> show errors;
+-------+------+---------------------------------------------------------------------------+
| Level | Code | Message                                                                   |
+-------+------+---------------------------------------------------------------------------+
| Error | 1123 | Can't initialize function 'clone'; Plugin initialization function failed. |
+-------+------+---------------------------------------------------------------------------+
1 row in set (0.00 sec)

- excerpt from error log

019-07-23T07:42:22.799789Z 7 [ERROR] [MY-013272] [Clone] Plugin Clone reported: 'Client: PFS table creation failed.'
2019-07-23T07:42:22.799822Z 7 [ERROR] [MY-010202] [Server] Plugin 'clone' init function returned error.
2019-07-23T07:42:22.799835Z 7 [Note] [MY-010733] [Server] Shutting down plugin 'clone'