RFR: JDK-8273815: move have_special_privileges to os_posix for POSIX platforms [v2]

[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

Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:

  Simplification proposed by Thomas Stuefe

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5540/files
  - new: https://git.openjdk.java.net/jdk/pull/5540/files/3e48d8cf..ed47cb34

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5540&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5540&range=00-01

  Stats: 6 lines in 1 file changed: 0 ins; 5 del; 1 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