RFR: 8350497: os::create_thread unify init thread attributes part across UNIX platforms

[Matthias Baesken]

In os::create_thread the 'init thread attributes' part of the method should be unified across UNIX platforms, e.g. regarding return code checking.

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Commit messages:
 - JDK-8350497

Changes: https://git.openjdk.org/jdk/pull/23746/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23746&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350497
  Stats: 12 lines in 2 files changed: 9 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/23746.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23746/head:pull/23746

PR: https://git.openjdk.org/jdk/pull/23746