RFR (trivial) 8197789: os::SuspendedThreadTask causes references to global operator delete

[Kim Barrett]

> On Feb 13, 2018, at 7:28 PM, coleen.phillimore at oracle.com wrote:
> 
> Summary: make destructor non-virtual and protected
> 
> Tested through mach5 tier1, and closed tests.
> 
> open webrev at http://cr.openjdk.java.net/~coleenp/8197789.01/webrev
> bug link https://bugs.openjdk.java.net/browse/JDK-8197789
> 
> Thanks,
> Coleen

Looks good, and trivial.