Apple announced today the forthcoming release of Macs based on Apple Silicon. Apple will bring support for this new target to open source in both the Clang and Swift compilers, as well as LLDB. The process will start immediately.
The first step will be to upstream support for the new Mac target to the LLVM project. The first patch is up for review.
Afterward, the corresponding changes will land in the Swift project (compiler, SwiftPM, Standard Library, etc).