It seems like we've lost compatibility with Xcode 8. We should fix that so Carthage will build correctly on macOS Sierra.
I'm working on it.
I tried today to add the the library from https://github.com/ZipArchive/ZipArchive on an XCode 8 Beta 6 project (using Swift 3), and got the following message when linking:
"The following binaries use incompatible versions of Swift"
This issue is about compiling Carthage itself with Xcode 8.
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I'm working on it.