RFR: 8357425: (fs) SecureDirectoryStream setPermissions should use fchmodat

[Brian Burkhalter]

Modify to use the `fchmodat(2)` system call to set permissions where possible to do so. This fixes the problem presented in the issue description.

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Commit messages:
 - 8357425: (fs) SecureDirectoryStream setPermissions should use fchmodat

Changes: https://git.openjdk.org/jdk/pull/25534/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25534&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357425
  Stats: 125 lines in 4 files changed: 113 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/25534.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25534/head:pull/25534

PR: https://git.openjdk.org/jdk/pull/25534