$ git clone -n https://src.fedoraproject.org/rpms/glibc.git /var/lib/mock/f41-build-side-1-2750628-31056/root/chroot_tmpdir/scmroot/glibc
Cloning into '/var/lib/mock/f41-build-side-1-2750628-31056/root/chroot_tmpdir/scmroot/glibc'...
$ git fetch origin 39bab0c46f64a4e785f33275c94f65e49f8f6271:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/glibc
 * [new ref]         39bab0c46f64a4e785f33275c94f65e49f8f6271 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 39bab0c Auto-sync with upstream branch master