RFR: JDK-8324682 Remove redefinition of NULL for XLC compiler [v6]

[Kim Barrett]

On Fri, 8 Mar 2024 09:07:23 GMT, Suchismith Roy <sroy at openjdk.org> wrote:

>> Remove redefinition of NULL for XLC compiler
>> In globalDefinitions_xlc.hpp there is a redefinition of NULL to work around an issue with one of the AIX headers (<dirent.h>). 
>> Once all uses of NULL in HotSpot have been replaced with nullptr, there is no longer any need for this, and it can be removed.
>> 
>> 
>> JBS ISSUE : [JDK-8324682](https://bugs.openjdk.org/browse/JDK-8324682)
>
> Suchismith Roy has updated the pull request incrementally with one additional commit since the last revision:
> 
>    update copyright

Looks good.

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Marked as reviewed by kbarrett (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18064#pullrequestreview-1931726118