RFR: 8253332: ZGC: Make heap views reservation platform independent [v2]

[Stefan Karlsson]

> ZVirtualMemoryManager::reserve_contiguous_platform tries to reserve three views of a given address range. The posix and
> windows versions are more or less duplicates, with calls to platform dependent versions of reserve/unreserve functions.
> I'd like to clean this up in preparation of an alternative implementation for heap memory allocation on Windows.
> 
> I choose to prefix the OS dependent functions with os_. For consistency, initialize_os should have been renamed as
> well, but the plan is to change that in a separate patch that splits that function into two, so I skipped it for now.

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/236/files
  - new: https://git.openjdk.java.net/jdk/pull/236/files/1a071cbf..25097139

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=236&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=236&range=00-01

  Stats: 4 lines in 2 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/236.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/236/head:pull/236

PR: https://git.openjdk.java.net/jdk/pull/236