`jsArguments()` is lowered into a reference of the `arguments` object.
This is useful for extracting varargs, when calling Kotlin code from
JavaScript. For a concrete example, see KT-15223.
Suppress "UNUSED_PARAMETER" to fix compilation warnings. Also suppress
"unused" to make the file less yellow in the IDE.
Also enable `-Werror`, unless Gradle property
`kotlin.build.disable.werror` is set to true.