RFR: 8261072: AArch64: Fix MacroAssembler::get_thread convention [v2]

[Anton Kozlov]

> Please review a fix in a special calling convention for aarch64_get_thread_helper for non-Linux platforms (windows/aarch64 for now). 
> 
> Preliminary review: https://mail.openjdk.java.net/pipermail/aarch64-port-dev/2021-January/011239.html

Anton Kozlov has updated the pull request incrementally with one additional commit since the last revision:

  Change comment

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2451/files
  - new: https://git.openjdk.java.net/jdk/pull/2451/files/217d3c23..3b111ae5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2451&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2451&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2451.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2451/head:pull/2451

PR: https://git.openjdk.java.net/jdk/pull/2451