Update Tanka to the latest release.
Change `meta.homepage` to point to the Tanka website instead of the
GitHub repository.
Add the `subPackage` attribute and additional ldflags arguments to
`buildFlagsArray`. Both are needed to fix the issue where `tk --version`
would print `dev` instead of the version string. The ldflags arguments
were copied from the Makefile in the Tanka repository.