[foreign-abi] RFR: Fix Aarch64 build failure

[Maurizio Cimadamore]

This patch addresses a build issue in aarch64 following a recent merge.

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Commit messages:
 - Fix aarch64 build failure

Changes: https://git.openjdk.java.net/panama-foreign/pull/390/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=390&range=00
  Stats: 15 lines in 4 files changed: 12 ins; 3 del; 0 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/390.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/390/head:pull/390

PR: https://git.openjdk.java.net/panama-foreign/pull/390