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

[David Holmes]

A trivial refactoring with zero functional changes.

The runtime exit code (os::shutdown, os::abort and os::die) on POSIX platforms is almost identical - Linux has one extra action in os::abort. This code should be shared via os_posix.cpp (note os::exit is already shared via os_posix.inline.hpp). 

Testing: 
  - GHA
  - Tiers 1-3

Thanks,
David

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Commit messages:
 - 8263564: Consolidate POSIX code for runtime exit support: os::shutdown, os::abort and os::die

Changes: https://git.openjdk.java.net/jdk/pull/2998/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2998&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263564
  Stats: 207 lines in 4 files changed: 55 ins; 152 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2998.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2998/head:pull/2998

PR: https://git.openjdk.java.net/jdk/pull/2998