RFR: 8261579: AArch64: Support for weaker memory ordering in Atomic [v6]

[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 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 16 additional commits since the last revision:

 - Merge branch 'master' into aarch64_acq_rel_cas
 - Update src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.S
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - Update src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.S
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - Update src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.S
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - Update src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.S
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - Update src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.S
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - Update src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.S
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - Update src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.hpp
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - Update src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.hpp
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - Update src/hotspot/cpu/aarch64/atomic_aarch64.hpp
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - ... and 6 more: https://git.openjdk.java.net/jdk/compare/dac70d7e...e2327629

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4597/files
  - new: https://git.openjdk.java.net/jdk/pull/4597/files/e691806f..e2327629

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4597&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4597&range=04-05

  Stats: 35202 lines in 671 files changed: 17658 ins; 15651 del; 1893 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