message: Set cwd for latexmk to dirname(rootDir)
  When using subfiles, we set the cwd for running latexmk to the directory
  of the rootFile and not the directory of the current subfile.
  This requires to add '-cd' to latexmk
diff: @@ -250,7 +250,13 @@ export class Builder {
  }
  this.currentProcess = cp.spawn(command, [], {cwd: path.dirname(rootFile), env: envVars, shell: true})
  } else {
  - this.currentProcess = cp.spawn(steps[index].command, steps[index].args, {cwd: path.dirname(rootFile), env: envVars})
  + let workingDirectory: string
  + if (steps[index].command === 'latexmk' && rootFile === this.extension.manager.localRootFile && this.extension.manager.rootDir) {
  + workingDirectory = this.extension.manager.rootDir
  + } else {
  + workingDirectory = path.dirname(rootFile)
  + }
  + this.currentProcess = cp.spawn(steps[index].command, steps[index].args, {cwd: workingDirectory, env: envVars})
  }
  const pid = this.currentProcess.pid
  this.extension.logger.addLogMessage(`LaTeX build process spawned. PID: ${pid}.`)
  