Git repos with large submodules

[raingloom]

Hey all!

So, I recently gave a go to packaging EDK2 on my channel, and found out
that it requires several submodules, including OpenSSL, which take up
quite a bit of space and take way longer to download than necessary.

Since I couldn't find a way to shallow-init the submodules, I added
them as separate origins and copied / symlinked them after the unpack
phase.

Is there a better way to do this? I don't see any equivalent of
--shallow-submodules in guile-git or libgit2.

I was thinking of writing a bit of Scheme to handle importing git repos
with their submodules as origins, but that feels like a rather ugly
hack.
Maybe libgit or guile-git would be the best layer to fix this at.