[jdk15u-dev] RFR: 8253638: Cleanup os::reserve_memory and remove MAP_FIXED

Fri Nov 5 19:29:08 UTC 2021

This backport is a part of MacOS/aarch64 support backport. It is needed to backport [JDK-8234930](https://bugs.openjdk.java.net/browse/JDK-8234930). 

It has been tested (tier1) on Linux x64 and x86, on Windows x64 and on MacOS x64 (https://github.com/KaperD/jdk15u-dev/actions/runs/1399380363)

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Commit messages:
 - Backport 625a9352bfdc017f426c3bd2a5c24b0f7598ccce

Changes: https://git.openjdk.java.net/jdk15u-dev/pull/125/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk15u-dev&pr=125&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253638
  Stats: 143 lines in 17 files changed: 29 ins; 57 del; 57 mod
  Patch: https://git.openjdk.java.net/jdk15u-dev/pull/125.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk15u-dev pull/125/head:pull/125

PR: https://git.openjdk.java.net/jdk15u-dev/pull/125