[jdk21u-dev] RFR: 8357793: [PPC64] VM crashes with -XX:-UseSIGTRAP -XX:-ImplicitNullChecks

[Martin Doerr]

Almost clean backport of [JDK-8357793](https://bugs.openjdk.org/browse/JDK-8357793). I only had to change `SharedRuntime` to `StubRoutines` because [JDK-8337987](https://bugs.openjdk.org/browse/JDK-8337987) is not in 21.

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Commit messages:
 - Backport ba9f44c90fe8da2d97d67b6878ac2c0c14e35bd0

Changes: https://git.openjdk.org/jdk21u-dev/pull/1842/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1842&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357793
  Stats: 4 lines in 2 files changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1842.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1842/head:pull/1842

PR: https://git.openjdk.org/jdk21u-dev/pull/1842