It crashes with Not_found error.

To reproduce,

module Js = {
  let f = () => 1
}

let x = Js.f()

Playground,
https://rescript-lang.org/try?version=v11.1.3&code=LYewJgrgNgpgBAKQM5wLxwN4Cg51gFzgDM04AKASjQD44BGLAXyywLgA9TkA6IyrIA

Instead of crashing, we should probably throw a better error that a module can't be named Js or something (since we already have Js module).