RFR: 8303002: Reject packed structs from linker [v4]

[Jorn Vernee]

> 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.

Jorn Vernee has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'PR_21' into RejectPacked
 - add javadoc + fixes for trailing padding
 - fix check for padding. Add check for trailing padding too
 - Reject packed structs and structs with extra padding
 - Check byte order of layouts passed to linker

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/13164/files
  - new: https://git.openjdk.org/jdk/pull/13164/files/0698b9e3..819214b2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13164&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13164&range=02-03

  Stats: 20894 lines in 676 files changed: 10200 ins; 7269 del; 3425 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