RFR: 8230664: Fix TestInstanceKlassSize for PowerPC [v2]

[Ziviani]

On Thu, 1 Oct 2020 12:21:22 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> I think this fix deserves a new JBS issue. It doesn't resolve the rounding problem described in JDK-8230664. It fixes
> an additional issue. The rounding problem may reoccur when other class layout changes are done.

Totally agreed. But, would you mind to create the ticket for me, please? Then, I change the commit header/message.
Thank you!!

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PR: https://git.openjdk.java.net/jdk/pull/358