RFR: 8321937: GenShen: Sync up 21u based repo [v3]

[Kelvin Nilsen]

On Wed, 13 Dec 2023 21:47:37 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Backport recent Shenandoah changes
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove use of option which has not been backported yet

Thanks for wading through all these diffs.

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Marked as reviewed by kdnilsen (Committer).

PR Review: https://git.openjdk.org/shenandoah-jdk21u/pull/4#pullrequestreview-1782562933