RFR: 8266453: Shenandoah: Some tests failed on MacOSX/AArch64

[Zhengyu Gu]

Some of tier1/tier2 tests failed on MacOSX/AArch64. The fix is similar to what JDK-8265984 does for ZGC.

Test:
  tier1 and tier2 with Shenandoah GC on MacOSX/AArch64

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Commit messages:
 - v1

Changes: https://git.openjdk.java.net/jdk/pull/3843/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3843&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266453
  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3843.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3843/head:pull/3843

PR: https://git.openjdk.java.net/jdk/pull/3843