RFR(sh/jdk8): [backport] 8231087: Shenandoah: Self-fixing load reference barriers for C1/C2

[Roman Kennke]

2nd attempt:

Issue:
https://bugs.openjdk.java.net/browse/JDK-8231087

Backport:
http://cr.openjdk.java.net/~rkennke/JDK-8231087-jdk8/webrev.01/

This time includes the actual C1 stuff (depended on JDK-8228369).

Let's include a few follow-ups:

https://bugs.openjdk.java.net/browse/JDK-8233165
http://cr.openjdk.java.net/~rkennke/JDK-8233165-jdk8/webrev.00/

and

https://bugs.openjdk.java.net/browse/JDK-8233021
http://cr.openjdk.java.net/~rkennke/JDK-8233021-jdk8/webrev.00/

and

https://bugs.openjdk.java.net/browse/JDK-8238153
http://cr.openjdk.java.net/~rkennke/JDK-8238153-jdk8/webrev.00/

Can I please get a review?

Thanks,
Roman