RFR: 8272811: Document the effects of building with _GNU_SOURCE in os_posix.hpp

[David Holmes]

On Tue, 24 Aug 2021 18:28:12 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> Please review this trivial code documentation enhancement based on discussions here:
>> 
>> http://mail.openjdk.java.net/pipermail/jdk-dev/2021-August/005946.html
>> 
>> Thanks,
>> David
>
> Looks OK to me, but I think the REF title should use "effects" :-)

@iklam thanks for taking a look.  Hmmmm tricky one. I think you are right. Using -D_GNU_SOURCE affects the build, but we are documenting the results of that and those are the effects of using the flag.

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PR: https://git.openjdk.java.net/jdk/pull/5212