RFR: 8337786: Fix simple -Wzero-as-null-pointer-constant warnings in aarch64 code

[Kim Barrett]

On Mon, 5 Aug 2024 14:48:55 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Please review this trivial change that replaces some uses of literal 0 as a
>> null pointer constant in aarch64 code to instead use nullptr.
>> 
>> Testing: mach5 tier1
>
> Looks fine.

Thanks for reviews @shipilev and @tschatzl

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PR Comment: https://git.openjdk.org/jdk/pull/20454#issuecomment-2272070131