Over the weekend, cordova-ios 8.0.0 was released with several breaking changes. We’ve discovered a few that have affected our systems and are working to fix this. However, many plugins are also not compatible. We’ve submitted a PR for cordova-plugin-firebasex but there are sure to be several more that need to be updated. For the moment we suggest using the following line in your config.xml if you are having iOS build issues:
<engine name="ios" spec="7.1.1" />
This line needs to be at the top level - not nested in a platform tag. Please let us know if you find other plugins that are experiencing issues.