Allow setting an alternate kotlinc binary (or use kotlinc-jvm)

[cgruber]

In some situations, notably in some package managers like hermit, which have installers which don't add the "kotlinc" binary so they won't have kotlin-native and kotlin-regular packages conflict, they end up with someone needing to explicitly point at "kotlinc-jvm" to invoke it. kscript makes an assumption that "kotlinc" will exist in "KOTLIN_HOME" and that isn't always true.

Is there a possibility to allow for a "--kotlinc-binary" flag so an alternative can be used. Or switch kscript to use kotlinc-jvm if that is, indeed, the actual dependency?