RFR: 8323629: Shenandoah: Fix missing include and declaration

[Kelvin Nilsen]

On Thu, 11 Jan 2024 23:59:04 GMT, William Kemper <wkemper at openjdk.org> wrote:

> There are some small changes for style guide conformance here.

Marked as reviewed by kdnilsen (no project role).

Note GHA testing failures.

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PR Review: https://git.openjdk.org/jdk/pull/17384#pullrequestreview-1818339840
PR Comment: https://git.openjdk.org/jdk/pull/17384#issuecomment-1889302162