[jdk21u-dev] RFR: 8331421: ubsan: vmreg.cpp checking error member call on misaligned address

[Martin Doerr]

Backport of [JDK-8331421](https://bugs.openjdk.org/browse/JDK-8331421). Clean except a difference in replaced code because [JDK-8309685](https://bugs.openjdk.org/browse/JDK-8309685) is not in 21u.

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Commit messages:
 - Backport beebce044db97e50a7aea3f83d70e134b2128d0a

Changes: https://git.openjdk.org/jdk21u-dev/pull/686/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=686&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331421
  Stats: 4 lines in 2 files changed: 1 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/686.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/686/head:pull/686

PR: https://git.openjdk.org/jdk21u-dev/pull/686