Kotlin compile error "unresolved reference" only when compiling from command line

I have the Kotlin code:

import com.google.gson.Gson
import java.io.File

class System {

    /*
Save current game state to file
 */
    internal fun saveGameState(game: Game) {
        val gameState = game.getGameState()
        val gson = Gson()
        val jsonString = gson.toJson(gameState)
        val pathname = FILENAME_SAVED_GAME
        File(pathname).writeText(jsonString)
    }

    private fun loadGameState(): Game {
        val jsonString = File(FILENAME_SAVED_GAME).readText(Charsets.UTF_8)
        val gson = Gson()
        val gameState: GameState = gson.fromJson(jsonString, GameState::class.java)
        File(FILENAME_SAVED_GAME).delete()
        return Game(gameState)
    }
...
}

When I run it from within IntelliJIDEA, it compiles and runs fine, including using this class to save state and restore state.

When I compile it from the command line, I use this command:

kotlinc *.kt -include-runtime -d GizmosK.jar

and I this error message:

System.kt:1:12: error: unresolved reference: google
import com.google.gson.Gson
           ^
System.kt:11:20: error: unresolved reference: Gson
        val gson = Gson()
                   ^
System.kt:19:20: error: unresolved reference: Gson
        val gson = Gson()
                   ^

I've successfully used this command many times before, but possibly not since adding this System class, which is the only one that imports anything from outside my project.

I've searched, and found this question which appears very similar to my problem, but I have a few concerns.

First, I don't know if this solution applies to my situation since my code is pure Kotlin and not Android.

Second, I don't know how to generalize their solution and make it apply to my situation. Like, I know I probably have to replace something with google.gson or com.google.gson or com.google.gson.Gson in there somewhere, but I don't know where, since there are three things there that look like package names. Do I need all three? I also don't know if expressions like package_name are literal strings I should enter verbatim or if I should replace those words with the actual package name.

Third, I've never had to specify flovar/flavor nor resource_package before in a command line, and I don't want to introduce new variables, if at all possible.

BTW, I'm compiling from the command line to generate a .jar file to distribute so anyone can run it from the command line without sharing my code or installing IntelliJIDEA.