When an iOS project is created and a plugin with custom frameworks is added on Windows, the path separator in FRAMEWORK_SEARCH_PATHS of the pbxproj file is incorrect. It has the Windows path separator. This causes build issues when the project is moved to OSX and built in Xcode.
This is ultimately coming from the xcode npm package. I have opened up an issue with that module with a suggested solution: https://github.com/alunny/node-xcode/issues/80
Once it is fixed there, we will need to refresh our version of the xcode npm package in our node_modules for cordova-ios