[11u] AArch64: Support for LSE atomics C++ HotSpot code

[Andrew Haley]

This is the first of two patches which allow C++ code in HotSpot
to use Arm's Large System Extensions.

This is necessary because some recent AArch64 hardware performs
very badly, particularly under heavy contention, with the older
way of doing atomic updates, using LDXR and STXR. Java code has
been using these LSE instructions, where available, for several
years.

This first patch is mostly just scaffolding: the actual performance
improvement is https://bugs.openjdk.java.net/browse/JDK-8261649.

The original patch did not apply because the argument order of
class Atomic functions changed with 8234740. Otherwise, it was
fairly straightforward.

http://cr.openjdk.java.net/~aph/8261027-jdk11u/

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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