Update to Swift 5.3.3, drop support for 32-bit platforms

This release brings the cross compilers up to Swift 5.3.3. The build scripts should now accept configurations for versions forward from 5.2. (Sorry it took so long). Since the release of 5.2 it has been impossible to build 32-bit swift for the arm-v7 and arm-v6 platforms, so for this release the 32-bit versions have been dropped. Sorry about that too. Ubuntu 18.02 bionic is the still the basis for the included swift runtimes. With 5.4 support I plan to transition to Ubuntu 20.04.

The arm64 x-compiler will build executables which, when linked with the included runtime libs, will run on either Raspberry Pi 3 or 4 or Apple M1 devices running docker. The two source projects included here demonstrate building for those environments.

The amd64 x-compiler will build executables which, when linked with the included runtime libs, will run on either x86-64 devices running Linux or on Apple Intel devices running docker. The two source projects included here demonstrate building for those environments.

Note that the intended use case of both packages is to generate SCRATCH docker images which can be run on their respective target. You don't have to base your docker image on SCRATCH, but if you don't you will need to base on an Ubuntu Bionic image and make sure that the Swift runtime libs included in this package are ahead of the native packages in the linker search path.

You may want to check out the companion project to this one ( https://github.com/CSCIX65G/swift-remote-debug.git ) for example Docker build files which build working Swift docker images.

If none of that sounds familiar, x-compiling may not be for you.