RFR: 8266440: Shenandoah: TestReferenceShortcutCycle.java test failed on AArch64 [v2]

[Zhengyu Gu]

> JDK-8263427 missed corresponding changes for aarch64.
> 
> LRB needs to be enabled during weak roots/references processing, regardless if heap is stable.
> 
> Test:
> 
> - [x] hotspot_gc_shenandoah on Macosx/AArch64
> - [ ] hotspot_gc_shenandoah on Linux 64/AArch64

Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:

  v2

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3902/files
  - new: https://git.openjdk.java.net/jdk/pull/3902/files/fea11bc4..4bb453b9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3902&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3902&range=00-01

  Stats: 11 lines in 1 file changed: 0 ins; 7 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3902.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3902/head:pull/3902

PR: https://git.openjdk.java.net/jdk/pull/3902