SDK 4.x doesn't generate war files. Even previous version of sdk 3.x also does't generate war files as far as i know. However with sdk3.x you had option to create overlay project and build a custom war file by adding your customization to alfresco/share war files.
SDK4.x is totally based on docker, so it is recommended to use its capabilities meant for docker based environment.
All your customizations are automatically applied to base alfresco/share docker images and containers are launched.
Even if you are planning to use standlone instances (installed via distribution method), you can opt to deploy your customization jar files under "module/share", "module/platform" as stated here: https://docs.alfresco.com/6.2/concepts/dev-extensions-packaging-techniques-jar-files.html
or use: https://docs.alfresco.com/6.2/concepts/dev-extensions-packaging-techniques-amps.html if your customzations are in form of amp package.
Have a look at these docs:
If you are still looking for generating war files, you may give a try by creating overlayed war with your custom modules by using "content-services-community" artifact for community and "content-services" artifact for enterprise versions of ACS. And for share you can use "share" artifact. See the dependencies below.
<!-- ACS war artifact for community version -->
<!-- ACS war artifact for enterprise version -->
<!-- share war artifact for both community and enterprise versions -->
(ACSCE, AWS SAA, Azure Admin)