RFR: 8303002: Reject packed structs from linker [v7]

[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 pull request now contains 52 commits:

 - Merge branch 'master' into RejectPacked
 - restrictions -> characteristics
 - polish pt. 2
 - polish wording
 - review comments
 - fix TestIllegalLink
 - Merge branch 'PR_21' into RejectPacked
 - Merge pull request #3 from JornVernee/IsForeignLinkerSupported
   
   rename has_port
 - rename has_port
 - Merge pull request #2 from JornVernee/WSL_BB
   
   account for missing functional in WSL in TestByteBuffer
 - ... and 42 more: https://git.openjdk.org/jdk/compare/b827ce83...df9f2eb2

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Changes: https://git.openjdk.org/jdk/pull/13164/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13164&range=06
  Stats: 161 lines in 11 files changed: 146 ins; 0 del; 15 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