Launches a new process with the given command.
This is almost same as `child_process.spawn`.

This returns a `ChildProcess` instance.
`kill` method of the instance kills the new process and its sub processes.

@param {string} command - The command to run.
@param {string[]} args - List of string arguments.
@param {object} options - Options.
@returns {ChildProcess} A ChildProcess instance of new process.
@private
function spawnCommandWithKill(...args) {
  const child = spawnCommand(...args)
  child.kill = kill.bind(child)
  return child
}