DSL code to handle ClojureScript compiler options


(build <arachne-id> compiler-opts)
Define an asset pipeline component which builds ClojureScript.

Arguments are:

- arachne-id (optional): the Arachne ID of the component
- compiler-options: A ClojureScript compiler options map. See the ClojureScript documentation
  for possible values. The only difference is that options which specify paths (:output-to,
  :output-dir, :preamble, :externs, etc.) will relative to the asset fileset rather than the
  process as a whole.

Returns the entity ID of the newly-created component.