RFR: JDK-8273815: move have_special_privileges to os_posix for POSIX platforms

[Matthias Baesken]

We have identical have_special_privileges() for Linux/AIX/BSD so the function is a good candidate to be moved to os_posix.

Thanks, Matthias

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Commit messages:
 - JDK-8273815

Changes: https://git.openjdk.java.net/jdk/pull/5540/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5540&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273815
  Stats: 50 lines in 4 files changed: 11 ins; 39 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5540.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5540/head:pull/5540

PR: https://git.openjdk.java.net/jdk/pull/5540