RFR: 6000: Get rid of build warnings in the JMC agent

[Guru]

Hi,

Please review the fix for 
JBS : https://bugs.openjdk.java.net/browse/JMC-6000 <https://bugs.openjdk.java.net/browse/JMC-6000>
PR : https://github.com/openjdk/jmc/pull/103 <https://github.com/openjdk/jmc/pull/103>

Thanks,
Guru