Fixes bug 26480; bug appeared when we re-enabled the geoip tests on
windows. Bug originally introduced by our fix to 25787; bug not in
any released Tor.
When I wrote the first one of these, it needed the path of the geoip
file. But that doesn't translate well in at least two cases:
- Mingw, where the compile-time path is /c/foo/bar and the
run-time path is c:\foo\bar.
- Various CI weirdnesses, where we cross-compile a test binary,
then copy it into limbo and expect it to work.
Together, these problems precluded these tests running on windows.
So, instead let's just generate some minimal files ourselves, and
test against them.
Fixes bug 25787
