`--jvm` flag

[armanbilge]

Is your feature request related to a problem? Please describe. Sometimes I have a script with //> using platform "js" but I would like quickly run it on JVM to compare behavior (I work a lot on cross-compiling libraries to have identical cross-platform semantics).

Describe the solution you'd like There are already flags --js and --native, so it seems fitting to have --jvm.

Describe alternatives you've considered I could not specify the platform in a directive, and always pass by command-line. But directives are very convenient :)