Unresolved reference when using Kotlin source files with a standalone compiler (kotlinc)

Hi,

I'm trying to use this extension with a simple, standalone Kotlin source file. The file looks like this:

```
fun main() {
println("Hello, world!")
}
```

With this, I get an `Unresolved reference: printlnkotlin(UNRESOLVED_REFERENCE)`.

I have found some past issues that look similar:
https://github.com/fwcd/kotlin-language-server/issues/73
https://github.com/fwcd/kotlin-language-server/issues/58

But I'm still not sure what I should do to make this work. Is there some kind of setting I need to change in order to work with standalone files?

I also saw that one issue mentioned something akin to a default Gradle directory or something, but, somehow, I can't find that issue anymore. Anyway, assuming that I have a completely fresh setup that has never touched a Gradle project, can I somehow make this work?

I have an installation of Android Studio, if that makes any difference. I have added the `kotlinc` and `Java` included with my Android Studio installation to my path, which enables me to compile my example file from the command line.