RFR: 8261649: AArch64: Optimize LSE atomics in C++ code

[Andrew Haley]

8261649: AArch64: Optimize LSE atomics in C++ code

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Commit messages:
 - Restore LSE CAS generation.
 - Merge https://github.com/openjdk/jdk into JDK-8261650
 - Trailing membar.
 - Flush everything correctly
 - Committed
 - Intermediate

Changes: https://git.openjdk.java.net/jdk/pull/2611/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2611&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261649
  Stats: 282 lines in 5 files changed: 166 ins; 51 del; 65 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2611.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2611/head:pull/2611

PR: https://git.openjdk.java.net/jdk/pull/2611