Yesterday the LLVM project created its release branch for version 6.0, and we plan to align with this branch for Swift 5.0. The swift-llvm, swift-clang, and swift-compiler-rt repos on GitHub have been updated with new branches named "swift-5.0-branch" that track the LLVM 6.0 branches.
On Monday (Jan. 8), we plan to create a preliminary swift-5.0-branch for Swift as well. This will allow us to get started setting up infrastructure to support the Swift 5 release. There will be additional information about the Swift 5 release and branching in the future. For now, you can safely ignore this branch.
Note that because the LLVM 6.0 release is just getting started, we’re going to hold off switching over to use it for a little while. The “stable” branches for the swift-llvm, swift-clang, and swift-compiler-rt repos will continue to merge from swift-4.1-branch for a while longer.