SwiftCrypto with backwards deployment support. Support macOS 10.10 / iOS 8.0 / tvOS 9.0 / watchOS 2.0.
For backwards deployment, set environment variable SWIFT_CRYPTO_BACK_DEPLOY.
$ export SWIFT_CRYPTO_BACK_DEPLOY="YES"
# for CLI tools, execute with env variable
$ swift ...
$ xcodebuild ...
# for Xcode GUI, reopen Xcode with env variable
$ killall Xcode
$ open Package.swift