RFR: 8253418: ZGC: Use pd_ prefix to denote platform dependent code [v2]

[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 incrementally with one additional commit since the last revision:

  Review 1

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/283/files
  - new: https://git.openjdk.java.net/jdk/pull/283/files/ec3fbf28..b3745a3b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=283&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=283&range=00-01

  Stats: 22 lines in 8 files changed: 0 ins; 0 del; 22 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