RFR: 8261579: AArch64: Support for weaker memory ordering in Atomic [v3]

[Andrew Haley]

> At present the Atomic operations in HotSpot only support conservative (the very strongest) and relaxed (the weakest) memory ordering.
> We should add at least seq_cst for LSE. This patch also adds a release-only CAS, needed for Shenandoah.

Andrew Haley has updated the pull request incrementally with one additional commit since the last revision:

  Sanitize memory order for BSD CAS

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4597/files
  - new: https://git.openjdk.java.net/jdk/pull/4597/files/bf988ca0..bbf1a51a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4597&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4597&range=01-02

  Stats: 15 lines in 1 file changed: 14 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4597.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4597/head:pull/4597

PR: https://git.openjdk.java.net/jdk/pull/4597