RFR: 8323629: Shenandoah: Fix missing include and declaration

[Paul Hohensee]

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 phh (Reviewer).

Looks like GHA is hosed, but this PR is cosmetic and builds fine locally, so np.

-------------

PR Review: https://git.openjdk.org/jdk/pull/17384#pullrequestreview-1818688316
PR Comment: https://git.openjdk.org/jdk/pull/17384#issuecomment-1889658144