RFR: 8375738: Fix -Wzero-as-null-pointer-constant warnings in MacOSX/bsd code

[Erik Joelsson]

On Tue, 20 Jan 2026 18:40:10 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to MacOSX and bsd code to avoid using literal zero
> as a null pointer constant, instead using nullptr.
> 
> Also disable that warning when building the gtest framework with clang,
> similarly to what was done in JDK-8338154 for gcc.
> 
> Testing: mach5 tier1.  Also tested with additional build changes to enable the
> warning.

Marked as reviewed by erikj (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/29329#pullrequestreview-3683921917