RFR: 8253418: ZGC: Use pd_ prefix to denote platform dependent code [v3]

[Per Lidén]

On Mon, 21 Sep 2020 12:56:28 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> ZGC uses the suffixes _platform and _os to denote platform dependent code. It's more common to name these functions
>> with a pd_ prefix. I suggest that we do the same in ZGC.
>
> Stefan Karlsson has updated the pull request with a new target base due to a merge or a rebase. The pull request now
> contains two commits:
>  - Review 1
>  - 8253418: ZGC: Use pd_ prefix to denote platform dependent code

Marked as reviewed by pliden (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/283