It probably first makes sense to focus on a MinGW-based build, #1320, but after that we should go for "full" windows support:

• No non-standard Unix helper shims (Microsoft's own libc (msvcrt/urtc) does a fair amount of work and is still often fine though)
• Build with actual MSVC or LLVM in MSVC mode
  • which means using the regular Windows C++ ABI