RFR: 8248238: Implementation of JEP: Windows AArch64 Support [v10]

[Monica Beckwith]

> This is a continuation of https://mail.openjdk.java.net/pipermail/aarch64-port-dev/2020-August/009566.html
>  
> Changes since then:
> * We've improved the write barrier as suggested by Andrew [1]
> * The define-guards around R18 have been changed to `R18_RESERVED`. This will be enabled for Windows only for now but
>   will be required for the upcoming macOS+Aarch64 [2] port as well.
> * We've incorporated https://github.com/openjdk/jdk/pull/154 by @AntonKozlov in our PR for now and built the
>   Windows-specific CPU feature detection on top of it.
> 
> [1] https://mail.openjdk.java.net/pipermail/aarch64-port-dev/2020-August/009597.html
> [2] https://openjdk.java.net/jeps/8251280

Monica Beckwith has updated the pull request with a new target base due to a merge or a rebase. The pull request now
contains 24 commits:

 - Merge remote-tracking branch 'upstream/master' into jdk-windows
 - SA: update copyright
 - Fix graal codestyle
 - Reduce includes
 - Merge remote-tracking branch 'upstream/master' into jdk-windows
 - os_windows: remove duplicated UMA handling
 - test_safefetch{32,N} works fine on win+aarch64
 - cleanup for 8253539: Remove unused JavaThread functions for set_last_Java_fp/pc
 - cleanup for 8253457: Remove unimplemented register stack functions
 - Merge remote-tracking branch 'upstream/master' into jdk-windows
 - ... and 14 more: https://git.openjdk.java.net/jdk/compare/ec9bee68...a7cdaad6

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

Changes: https://git.openjdk.java.net/jdk/pull/212/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=212&range=09
  Stats: 2566 lines in 62 files changed: 2208 ins; 126 del; 232 mod
  Patch: https://git.openjdk.java.net/jdk/pull/212.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/212/head:pull/212

PR: https://git.openjdk.java.net/jdk/pull/212