RFR: 8253332: ZGC: Make heap views reservation platform independent [v3]

[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 2

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/236/files
  - new: https://git.openjdk.java.net/jdk/pull/236/files/25097139..bb10b9c2

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=236&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=236&range=01-02

  Stats: 15 lines in 4 files changed: 5 ins; 0 del; 10 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