Release 2019-08-28 toolchain for macOS. (#262)
Release 2019-08-28 toolchain for macOS. (#262)

https://github.com/apple/swift/commit/aa4fd5996192efa9d4caad5e6d597c3f882553f3

Remove 2019-08-25 toolchain, which had z3 linker issues.
tensorflow/swift,tensorflow/swift