This is for anyone who wants to try building the Swift 5.1.4 toolchain on an Android AArch64 device using the scripts in this repository. The following commands should do, you will need 5 GBs of free space and I estimate about an hour and a half with a Snapdragon 855:

pkg install clang binutils-gold file patch python cmake ninja python2 perl rsync libandroid-spawn libcurl libicu libsqlite libuuid libxml2 llbuild pkg-config
TERMUX_MAKE_PROCESSES=7 ./build-package.sh swift

Maybe one of the maintainers can build it and add the package to bintray.com. Getting all this cross-compiling from linux x86_64 like all the other Termux packages will require more work, since the Swift build scripts don't fully support building all this, other than cross-compiling the compiler and stdlib.

Most of these patches have been upstreamed and will be part of the upcoming 5.2 release next month. Only around 10 tests fail from the Swift compiler test suite of 10,000+ tests, with a couple more testing-related patches backported to this release. Where I used somebody else's patches from upstream, I included the full git commit info.

Once built, you can test it out by downloading a Swift package that has support for the Swift package manager and running swift build. I have tried it on a couple Swift packages and it worked well, as long as the package didn't import a bunch of C headers, which can sometimes vary for Bionic, or you didn't need to --enable-test-discovery when running swift test, which requires IndexStore added now.

Install the resulting deb package with dpkg -i debs/swift_5.1.4_aarch64.deb to make uninstalling the compiler with pkg uninstall swift easy later. I have not tried building with this pull on Android 7 or 8, let me know if you try it and that has any problems.