[jdk16u] RFR: 8263564: Consolidate POSIX code for runtime exit support: os::shutdown, os::abort and os::die

[Harold Seigel]

Please review this backport of JDK-8263564 to JDK-16u.  The original bug fix patch applied cleanly except for files os_linux.cpp and os_posix.cpp. But, the resulting hand merge resulted in code very similar to the original fix. After applying the patch to a JDK-16u repo and modifying the appropriate os_<..>.cpp files, the fix was regression tested by running Mach5 tiers 1 and 2 on Linux, Windows, and Mac OS, and running tiers 3-5 on Linux x64.

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Commit messages:
 - Backport 554dd29fb67b9a25ad161920b57e238c06024938

Changes: https://git.openjdk.java.net/jdk16u/pull/97/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16u&pr=97&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263564
  Stats: 210 lines in 4 files changed: 56 ins; 152 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk16u/pull/97.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16u pull/97/head:pull/97

PR: https://git.openjdk.java.net/jdk16u/pull/97