RFR: 8291067: macOS should use O_CLOEXEC instead of FD_CLOEXEC [v7]

[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 with a new target base due to a merge or a rebase. The pull request now contains 11 commits:

 - Merge master
 - rename test file to test_file.txt, so it's easy to determine the purpose of the artifact to however happens to be looking
 - use open() to create the test file as needed
 - create our own test file, to guarantee it will exist
 - remove comment, fix spacing
 - test on all platforms except Windows
 - add test to verify that open(O_CLOEXEC) implies FD_CLOEXEC on macOS
 - assume O_CLOEXEC on macOS
 - match existing code
 - add missing code from merge
 - ... and 1 more: https://git.openjdk.org/jdk/compare/cd6a203a...db9d11a3

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Changes: https://git.openjdk.org/jdk/pull/9663/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9663&range=06
  Stats: 51 lines in 2 files changed: 24 ins; 23 del; 4 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