RFR: 8345119: Some java/foreign tests wrongly assume aligned memory

[Quan Anh Mai]

Hi,

This patch resolves some issues I found that the tests wrongly assume sufficient alignment from the segment returned by `Arena::allocate`.

Please take a look and leave your reviews, thanks a lot.

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Commit messages:
 - Some java/foreign tests wrongly assume aligned memory

Changes: https://git.openjdk.org/jdk/pull/22415/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22415&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345119
  Stats: 16 lines in 2 files changed: 0 ins; 0 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/22415.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22415/head:pull/22415

PR: https://git.openjdk.org/jdk/pull/22415