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

[Stefan Karlsson]

> 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

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Changes: https://git.openjdk.java.net/jdk/pull/283/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=283&range=02
  Stats: 32 lines in 18 files changed: 0 ins; 0 del; 32 mod
  Patch: https://git.openjdk.java.net/jdk/pull/283.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/283/head:pull/283

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