RFR: JDK-8328272: [AIX] Use flag kind "diagnostic" for platform specific flags [v2]

[Joachim Kern]

> Current platform implementation (globals_aix.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.

Joachim Kern has updated the pull request incrementally with one additional commit since the last revision:

  keep MaxExpectedDataSegmentSize

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/18337/files
  - new: https://git.openjdk.org/jdk/pull/18337/files/261b7fcc..5cf1259a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18337&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18337&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18337.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18337/head:pull/18337

PR: https://git.openjdk.org/jdk/pull/18337