Clean up warnings about juice HOT 3 OPEN

I am for the _ addons, but it is hard to test since it depends on the backend selection which warnings are spawn.

from juice.

But yes, this is something definitely to be taken care of, especially to de-clutter the build process.

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that's a good point though, i really doubt rustc team want to try to untangle checking feature-conditional warnings automatically, so i doubt there's much we can do for the time being.

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