Well, that was fun; dbupdate doesn’t have a ./configure so I had to do it by hand, snarfing all the -l dependencies from the pkgconfig files. Anyway, here’s a .zip containing dbupdate.exe:
https://glenn.pulpitrock.net/dbupdate.zip
It’ll run in either msys2 bash or Windows cmd, like this:
$ dbupdate.exe 1 .
‘1’ is the database version you need, ‘.’ is the directory in which to put the version_x directory lensfun will be looking for. In this case, the current working directory.
You should put the executable in one of the directories of your $PATH…