RFR: 8291067: macOS should use O_CLOEXEC instead of FD_CLOEXEC [v6]

[Gerard Ziemski]

> O_CLOEXEC is also available on macOS (__DARWIN_C_LEVEL >= 200809L), so use it same as on linux.

Gerard Ziemski has updated the pull request incrementally with one additional commit since the last revision:

  rename test file to test_file.txt, so it's easy to determine the purpose of the artifact to however happens to be looking

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9663/files
  - new: https://git.openjdk.org/jdk/pull/9663/files/fe2c00f8..dd661815

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9663&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9663&range=04-05

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9663.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9663/head:pull/9663

PR: https://git.openjdk.org/jdk/pull/9663