[11] RFR: Fix AArch64, add Shenandoah parts of JDK-8216989

[Zhengyu Gu]

Okay.

-Zhengyu

On 9/4/19 4:31 AM, Aleksey Shipilev wrote:
> We have massive AArch64 failures in sh/jdk11 after recent merge, because we miss the
> Shenandoah-specific parts of JDK-8216989 [1] backport. This fixes it:
>    http://cr.openjdk.java.net/~shade/8216989/webrev.11-sh.01/
> 
> The shape of the affected method is a bit different in sh/jdk11, so I had to adapt it.
> 
> Testing: aarch64 hotspot_gc_shenandoah
>