RFR: 8259849: Shenandoah: Rename store-val to IU-barrier [v2]

[Aleksey Shipilev]

On Mon, 18 Jan 2021 10:05:14 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update copyright years in modified files
>
> This makes sense.

...except that GHA report these two tests have failed:
gc/shenandoah/options/TestWrongBarrierDisable.java 
gc/shenandoah/options/TestWrongBarrierEnable.java

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PR: https://git.openjdk.java.net/jdk/pull/2104