WARNING: :preloads should only be specified with :none optimizations

[sumbach]

In ClojureScript 1.9.854 and above, this warning is produced during lein doo clojurescript compilation for whitespace/simple/advanced optimizations:

WARNING: :preloads should only be specified with :none optimizations

1. This warning was added to ClojureScript 1.9.293; see CLJS-1821
2. ClojureScript 1.9.854 began adding a process.env preload by default; see CLJS-2280
3. The process.env preload is added twice because add-implicit-options is called twice:
   • https://github.com/bensu/doo/blob/eceb879affbdab190b535404c179a4acf67146b0/plugin/src/leiningen/doo.clj#L197
   • https://github.com/bensu/doo/blob/eceb879affbdab190b535404c179a4acf67146b0/plugin/src/leiningen/doo.clj#L223
     • https://github.com/clojure/clojurescript/blob/r1.9.854/src/main/clojure/cljs/build/api.clj#L205
       • https://github.com/clojure/clojurescript/blob/r1.9.854/src/main/clojure/cljs/closure.clj#L2469

I'm not familiar enough with doo or cljs internals to propose a solution, but here are a couple off-the-cuff ideas:

• Maybe keep a binding to the original compiler value in leiningen.doo/doo and pass this value to the cljs functions, while passing the result of add-implicit-options to doo.core functions as necessary.
• Or perhaps the add-implicit-options call could be moved to doo.core/assert-compiler-opts, assuming implicit options are not needed by doo.core/install! and doo.core/run-script.

Also, thank you, @bensu, for an amazing tool! lein doo is an incredible enabler for automated cljs testing 😀