RFR: 8248238: Implementation of JEP: Windows AArch64 Support [v8]

[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 incremental webrev
excludes the unrelated changes brought in by the merge/rebase. The pull request contains 22 additional commits since
the last revision:

 - 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
 - Update orderAccess_windows_aarch64.hpp
   
   changing from Acq-reL to Sequential Consistency to avoid compiler reordering when no ordering hints are provided
 - 8248787: G1: Workaround MSVC bug
   Reviewed-by:
   Contributed-by: mbeckwit, luhenry, burban
 - ... and 12 more: https://git.openjdk.java.net/jdk/compare/4dd32e55...275a0b7f

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/212/files
  - new: https://git.openjdk.java.net/jdk/pull/212/files/68f61d60..275a0b7f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=212&range=07
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=212&range=06-07

  Stats: 25771 lines in 386 files changed: 3908 ins; 20954 del; 909 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