Clojurians Log v2

We just got bit by :undeclared-var not being an error, but a warning. https://clojurescript.org/reference/compiler-options#warnings would it be a useful configuration to allow making some of these warnings errors by putting :error instead of a boolean? That could also align with https://clojurescript.org/reference/compiler-options#checked-arrays

FWIW shadow-cljs has :warnings-as-errors true or :warnings-as-errors #{:undeclared-var}, didn't want to change meaning of existing stuff

@dominicm pretty sure there's already a warning handler thing and you can use a namespaced symbol to do this

that is it could be made a little sugar-y but the functionality already exists