[URGENT] [8u] Re-cast JNI critical strings patch to be Shenandoah-specific

[Roman Kennke]

Looks good to me.

Roman


> There is a hard requirement for 8u-aarch64 integration that any 
> non-mainline patch in shared code
> was either trivial, or be obviously Shenandoah-specific. Unfortunately, 
> at least one of the changes
> affects the shared path. With this patch, I demote it to 
> Shenandoah-specific paths only.
> 
> This blocks 8u integration.
> 
> 8u webrev:
>    
> https://cr.openjdk.java.net/~shade/shenandoah/8u-jni-critical-strings/webrev.01/ 
> 
> 
> The resulting difference against 8u upstream would be:
>    
> https://cr.openjdk.java.net/~shade/shenandoah/8u-jni-critical-strings/8u-upstream.diff 
> 
> 
> Testing: hotspot_gc_shenandoah; minimal1 build (to test INCLUDE_ALL_GCS 
> path)
>