Apart from the CI failure, looks good to me. I guess they need some better cross-compiling support, but hopefully you can override a build variable to get it to use the Win32 build during the ARM64 one?

Yep, looking into what else needs the override now.

Another trick we could use here is to extract the version number from the header file, that way we can go back to setting just the tags when building:

$ver = @{}
Get-Content .\generic\tcl.h | ?{ $_ -match '#\s*define\s+TCL_([A-Z]+)_VERSION\s+(\d+).*'} | %{ $ver[$Matches[1]] = $Matches[2] }
$ver.MAJOR
$ver.MINOR

That doesn't help people trying to build separately (without this script), but the current change doesn't help them either.

Hmm, could we actually do that in tcltk.props? I'm not too concerned about this solution being just for our purposes; once we do the update, the values in tcltk.props/tcl.vcxproj/tk.vcxproj will be right (for anyone sticking to the same version as us).

I think this is ready to go, but I'd rather someone else hit the big green button in this repo :)