[jdk11u-dev] RFR: 8253638: Cleanup os::reserve_memory and remove MAP_FIXED

[Vladimir Kempik]

Hello, please review this backport of JDK-8253638  to jdk11u-dev, its a prerequest for JDK-8255254 which is mac-aarch64 backport prerequest

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Commit messages:
 - 8253638: Cleanup os::reserve_memory and remove MAP_FIXED

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/574/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=574&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253638
  Stats: 159 lines in 18 files changed: 31 ins; 65 del; 63 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/574.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/574/head:pull/574

PR: https://git.openjdk.java.net/jdk11u-dev/pull/574