Alfred wrote "We don't require git for anything in the GNU project", and the obvious proof by contradiction is that we do require it for glibc development work on master. The answer "Tarball?" is not a supportable one because you're quickly so far away from master that you can't generate a diff that would apply.
Git still isn't a requirement to be able to contribute to glibc or the rest of the GNU project, you can pull the e.g. tarball, make a patch, and send it to libc-alpha. The change might be applicable to master, it might not, but that is the same situation if you checked out a copy of the glibc from a year back. It might make it easier to get the patch into mainline, but it still isn't a requirement.
