RFR: 8341336: Fix -Wzero-as-null-pointer-constant warnings in PRODUCT-only code

[Kim Barrett]

On Tue, 1 Oct 2024 16:53:03 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Please review this change that removes -Wzero-as-null-pointer-constant warnings
>> triggered by PRODUCT-only code. Most are uses of PRODUCT_RETURN0 in a pointer
>> context.  These are changed to use the (new) macro PRODUCT_RETURN_NULL.
>> 
>> Testing: mach5 tier1
>> Locally (linux-x64) ran tier1 testing on a release build.
>> (mach5 mostly does fastdebug testing)
>
> Marked as reviewed by stefank (Reviewer).

Thanks for reviews @stefank , @walulyai , and @shipilev

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PR Comment: https://git.openjdk.org/jdk/pull/21290#issuecomment-2389762364