Is your feature request related to a problem? Please describe.
I cannot update the MacPorts Portfile of openzl to version 0.2.0, because the submodules are not included.

Describe the solution you'd like
Please bundle the submodules in the release tarball.

Describe alternatives you've considered
Using git submodule update --init fails here as there is no .git file to be found anywhere in the release tree. Using cmake to fetch the submodules is not allowed on the MacPorts build bots, as there are no checksums.

Additional context
For example:

system -W /opt/local/var/macports/build/openzl-6926f5c8/work/openzl-0.2.0/deps/googletest "git submodule update --init googletest"
fatal: not a git repository (or any of the parent directories): .git
Command failed: git submodule update --init googletest
Exit code: 128