RFR: 8253690: [PPC64] Use flag kind diagnostic for platform specific flags

[Thomas Stuefe]

On Tue, 29 Sep 2020 20:49:01 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> Current platform implementation (globals_ppc.hpp) uses regular product flags for almost everything.
> Most platform specific flags were never intended for official support. They are only there to diagnose issues and find
> workarounds. So flag kind "diagnostic" fits better for them.
> 
> Note that I rearranged a couple of lines when looking at the diff.
> My actual change is what is described here: https://bugs.openjdk.java.net/browse/JDK-8253692

Looks good Martin.

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Marked as reviewed by stuefe (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/413