RFR: 8303002: Reject packed structs from linker

Mon Mar 27 13:59:17 UTC 2023

This patch adds checks in AbstractLinker to reject packed structs and structs with excess padding (e.g. unnamed bitfields), since both of those are currently not supported, and the ABI/spec seems too vague to base support on.

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Depends on: https://git.openjdk.org/jdk/pull/13161

Commit messages:
 - fix check for padding. Add check for trailing padding too
 - Reject packed structs and structs with extra padding

Changes: https://git.openjdk.org/jdk/pull/13164/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13164&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303002
  Stats: 73 lines in 4 files changed: 63 ins; 3 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/13164.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13164/head:pull/13164

PR: https://git.openjdk.org/jdk/pull/13164