RFR: 8377898: Hotspot build on AIX with unused-functions warning reports some unused functions

[Matthias Baesken]

When enabling the unused-functions warning on AIX (where clang is with xlC17), we get a couple of warnings as errors. Those should be fixed to be able to enable  unused-functions warnings  on gcc AND clang .

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Commit messages:
 - JDK-8377898

Changes: https://git.openjdk.org/jdk/pull/29715/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29715&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377898
  Stats: 13 lines in 2 files changed: 0 ins; 11 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/29715.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29715/head:pull/29715

PR: https://git.openjdk.org/jdk/pull/29715