Clojure uses reader conditionals https://clojure.org/guides/reader_conditionals that allow writing code that cross-compiles between different platforms, and generates platform specific code when necessary.

Many Clojure libraries cross-compile between Clojure and ClojureScript. You can see an example here https://github.com/yogthos/json-html/blob/master/src/json_ht...

Short answer - yes. https://clojurescript.org/

Yes, that's ClojureScript.