RFR(XXS): 8204561: JVM_GetClassSigners: wrap signers oop in an objArrayHandle for subsequent safepoint.

[Reingruber, Richard]

Hi,

could you please review the following webrev? It fixes an issue because of an unhandled oop in JVM_GetClassSigners.

Webrev: http://cr.openjdk.java.net/~rrich/webrevs/2018/8204561/webrev.01/
Bug:    https://bugs.openjdk.java.net/browse/JDK-8204561

The contribution needs to be sponsored as well.

Thanks, Richard.