import groovy.io.FileType
import com.cloudbees.groovy.cps.NonCPS

@NonCPS
def traverseHelper() {
    new File(pwd()).traverse(type: FileType.FILES) {
        println it.path
    }
}

pipeline {
    agent any
    stages {
        stage('Build') {
            steps {
                parallel(
                    "Linux": {
                        node(label: 'lnx') {
                            script {
                                //checking out from git here
                                traverseHelper()
                            }
                        }
                    },
                    "Windows": {
                        node(label: 'win') {
                            script {
                                //do Windows stuff here
                            }
                        }
                    }
                )
            }
        }
        //other stages here
    }
}