Apparently Tk has something in its e_capi.c file that does not work with the latest SDK (I guess they're redefining macros).

In master, we use prebuilt binaries, which is why this is not a problem. But we'll either need to fix Tk's sources or backport the code that uses the prebuilt binaries (just for Tcl and Tk - the OpenSSL part is not compatible) before we can merge this.

I'll try and take a look at it over the next few weeks. An a workaround, you should be able to "SET WindowsSDKVersion=10.0.16299.0" and pass "--no-tkinter" to build.bat to compile without the change.