RFR: JMC-6206: Making the agent prototype work on OpenJDK 11

[Marcus Hirt]

Hi all,

Please review this fix to get the early agent prototype to work on OpenJDK
11.

Jira:  https://bugs.openjdk.java.net/browse/JMC-6206
Patch: http://cr.openjdk.java.net/~hirt/JMC-6206/webrev.01/

Kind regards,
Marcus