Because, why not, right? However, I'm... not even sure what is necessary for it. Well, that's not entirely true -- I did read the file, and I got various packages for FreeBSD installed (including cmake and ninja). I ported libdispatch-913.60.2, and that's one of the current, ahem, sources of trouble -- the include files and libraries are in /usr/local, and I don't know how to tell the build system that it should check there. I assume I'm missing something very obvious, which, sadly happens with me.
I am building with:
% ./utils/build-script --skip-build-benchmarks --skip-build-cmark --skip-build-llvm --skip-build-foundation --skip-ios --skip-watchos --skip-tvos --swift-darwin-supported-archs
uname -m --release-debuginfo --swift-disable-dead-stripping --test