message: Add a repos .json file for github llvm-swift-5-transition.  I'm
  not sure if the swift URL is correct, but it's a starting point.
diff: {"name": "swift",
  "vcs": "git",
  "url": "https://github.com/apple/swift.git",
  - "ref": "master-llvm-swift5-transition"},
  + "ref": "swift-5.0-branch"},
  {"name": "cmark",
  "vcs": "git",
  