RFR: 8286446: PPC64: fix crashes after JDK-8284161 (virtual threads preview) [v2]

[Richard Reingruber]

> With this change `java -version` succeeds with the devkit build also the standard build on a ppc64le box does not crash anymore.
> 
> Also tier1 tests don't look too bad.

Richard Reingruber has updated the pull request incrementally with one additional commit since the last revision:

  Martin's feedback

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8617/files
  - new: https://git.openjdk.java.net/jdk/pull/8617/files/c1416e59..ed466a24

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8617&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8617&range=00-01

  Stats: 33 lines in 3 files changed: 3 ins; 27 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8617.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8617/head:pull/8617

PR: https://git.openjdk.java.net/jdk/pull/8617