RFR: 8300253: Introduce AArch64 nzcv accessors [v3]

[Erik Österlund]

> Some code, such as verification code, might want to run without changing the state of the system. To do that, it's useful to be able to get and set the nzcv flags. This enhancement aims at adding accessors for that.

Erik Österlund has updated the pull request incrementally with one additional commit since the last revision:

  Fix test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12038/files
  - new: https://git.openjdk.org/jdk/pull/12038/files/6dbd9871..fdae4a44

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12038&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12038&range=01-02

  Stats: 908 lines in 2 files changed: 22 ins; 0 del; 886 mod
  Patch: https://git.openjdk.org/jdk/pull/12038.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12038/head:pull/12038

PR: https://git.openjdk.org/jdk/pull/12038