RFR: 8369642: [ubsan] nmethod::nmethod null pointer passed as argument 2 to memcpy

[Chad Rakoczy]

[JDK-8316694](https://bugs.openjdk.org/browse/JDK-8316694) introduced a counter so that the nmethod immutable data can be shared between relocated nmethods to eliminate an unnecessary copy. The counter is aligned in memory so that must be taken into account when calculating the amount of memory used by the counter

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Commit messages:
 - Respect memory alignment for ImmutableDataReferencesCounter

Changes: https://git.openjdk.org/jdk/pull/27778/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27778&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369642
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/27778.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27778/head:pull/27778

PR: https://git.openjdk.org/jdk/pull/27778