Hi Ingo,
I am not sure if you can build for Windows, if not I can explain it to you. Laurent broke the Windows build completly with:
https://dev.gnupg.org/rLIBKLEOb45c40d99d864d43ad174702887b401e1bbdddaf
I tried some small fixes but they resulted in more errors. I don't understand what he broke there and I would like it if you could investigate and create a decent bug report or fix for this. I just reverted this.