Log exact command executed by ExternalJSEnv.

Author: nicolasstucki

js-envs/src/main/scala/org/scalajs/jsenv/ExternalJSEnv.scala

@@ -107,6 +107,8 @@ abstract class ExternalJSEnv(
       for ((name, value) <- vmEnv)
         pBuilder.environment().put(name, value)
 
+      logger.debug("Starting process: " + allArgs.mkString(" "))
+
       pBuilder.start()
     }