RFR: 8337784: Fix simple -Wzero-as-null-pointer-constant warnings in linux/posix code

[Kim Barrett]

On Mon, 5 Aug 2024 07:05:02 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Please review this trivial change that replaces some uses of literal 0 as a
>> null pointer constant in linux/posix code to instead use nullptr.
>> 
>> Testing: mach5 tier1
>
> Marked as reviewed by stefank (Reviewer).

Thanks for reviews @stefank and @shipilev .

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PR Comment: https://git.openjdk.org/jdk/pull/20452#issuecomment-2269503180