Roman's comments during code review of JDK-8225582, suggested that IN_NATIVE barrier is not proper wired in C1 and C2.

https://mail.openjdk.java.net/pipermail/shenandoah-dev/2019-June/009937.html

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I suspect you're gonna need the C1 and C2 IN_NATIVE barriers, esp. for
the CLDG roots. Should be relatively easy to wire up the LRB barriers
there (probably ask shade or roland). It will be more complex to do the
other parts and return NULL on unreachable objects, but this is not
needed yet. When we do, we should probably just make it call out to runtime.

Roman