RFR: 8316746: Top of lock-stack does not match the unlocked object

[Martin Doerr]

I think we need to support "Top of lock-stack does not match the unlocked object" and take the slow path. Reason: see JBS issue.
Currently only PPC64 code. I'd like to get feedback before implementing it for other platforms (needed for all platforms).

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Commit messages:
 - 8316746: Top of lock-stack does not match the unlocked object

Changes: https://git.openjdk.org/jdk/pull/15903/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15903&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316746
  Stats: 36 lines in 4 files changed: 13 ins; 11 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/15903.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15903/head:pull/15903

PR: https://git.openjdk.org/jdk/pull/15903