RFR (XS): Shenandoah: fix build failures after JDK-8244737 backport

[Aleksey Shipilev]

Hi,

Surprising to me, after integration to aarch64-port/jdk8u-shenandoah [1], CI suddenly started
reporting failures in Linux minimal1 and Windows builds. This is the fix:
  https://cr.openjdk.java.net/~shade/shenandoah/8u-fix-8244737.patch

This is 8u-speficic trouble. I would prefer to push it to aarch64-port/jdk8u-shenandoah/hotspot
directly to unbreak the integration repository. I would then pull it to shenandoah/jdk8.

Testing: windows-x86_64-server-fastdebug, linux-x86-minimal1-fastdebug builds

-- 
Thanks,
-Aleksey

[1] https://mail.openjdk.java.net/pipermail/aarch64-port-dev/2020-May/008970.html