For the record, "official" support is still not there because there's no CI environment for Windows (currently only macOS and a few versions of Ubuntu have CI). So changes aren't guaranteed to not break other platforms.
There's upstream (in-tree) support for Darwin, Linux, Windows, Cygwin, FreeBSD, Android, PS4, and Haiku. But most of those don't have CI support yet.
Same is true for architectures. There's support for ARM, i386, x86_64, PPC64 (BE + LE), and s390x.
IIRC there's been some talk about how to extend the CI infrastructure to support more executor environments, but so far I don't think it's been a high enough priority.