RFR: 8370314: Update signals_posix with new Linux signal codes

[David Holmes]

There are a few "new" si_codes defined on Linux that we did not support for error reporting. Some of these are only exposed in more recent glibc versions so we have to hard-wire them for older build environments.

The changes are all conditional on Linux, except the POLL_IN addition which is conditional on SIGPOLL, which is turn only exists on Linux.

Tested with local Linux environments, plus our CI plus GHA.

Thanks.

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Commit messages:
 -  8370314: Update signals_posix with new Linux signal codes

Changes: https://git.openjdk.org/jdk/pull/29105/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29105&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8370314
  Stats: 39 lines in 1 file changed: 38 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/29105.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29105/head:pull/29105

PR: https://git.openjdk.org/jdk/pull/29105