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

[Martin Doerr]

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

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Commit messages:
 - 8253690: [PPC64] Use flag kind diagnostic for platform specific flags

Changes: https://git.openjdk.java.net/jdk/pull/413/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=413&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253690
  Stats: 36 lines in 1 file changed: 11 ins; 10 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk/pull/413.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/413/head:pull/413

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