RFR: 8367085: Sort os/posix includes

[Francesco Andreuzzi]

In this PR I sort includes in `os/posix` using `SortIncludes.java`.

Passes `tier1`.

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Commit messages:
 - comments
 - sort

Changes: https://git.openjdk.org/jdk/pull/27141/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27141&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367085
  Stats: 32 lines in 8 files changed: 15 ins; 14 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/27141.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27141/head:pull/27141

PR: https://git.openjdk.org/jdk/pull/27141