I'm currently attempting to cross-compile the stdlib for Android using a macOS host. One snag is that apple/swift/CMakeLists.txt adds a SourceKit target if the host machine is Darwin, and does not add it if the host is Linux. I should be able to turn SourceKit builds on or off via the build-script.
Following the project's convention, this should probably be an option named --skip-build-sourcekit. On Linux, utils/build-script should pass this option by default. On Darwin, it should not.