RFR: 8291067: macOS should use O_CLOEXEC instead of FD_CLOEXEC [v2]

[Gerard Ziemski]

On Wed, 28 Sep 2022 17:21:53 GMT, Gerard Ziemski <gziemski at openjdk.org> wrote:

>> 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 two additional commits since the last revision:
> 
>  - add test to verify that open(O_CLOEXEC) implies FD_CLOEXEC on macOS
>  - assume O_CLOEXEC on macOS

Followed feedback from David and Thomas.

We now assume that `O_CLOEXEC` is available on macOS, but we added `__APPLE__` gtest that verifies that assumption via:

`make run-test TEST=gtest:os.open_O_CLOEXEC`

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