RFR: 8318127: align_up has potential overflow

[Casper Norrbin]

Hi everyone,

The `align_up` function contained code which could potentially overflow and produce an incorrect result. This PR adds an assert to check for such.

Additionally, a test case that previously caused an overflow has been updated to use the highest possible non-aligned value that does not trigger an overflow.

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Commit messages:
 - change reserve_memory test
 - align overflow check

Changes: https://git.openjdk.org/jdk/pull/20808/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20808&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318127
  Stats: 6 lines in 3 files changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/20808.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20808/head:pull/20808

PR: https://git.openjdk.org/jdk/pull/20808