$ git clone -n https://src.fedoraproject.org/rpms/openvdb.git /var/lib/mock/f40-build-781404-131566/root/chroot_tmpdir/scmroot/openvdb
Cloning into '/var/lib/mock/f40-build-781404-131566/root/chroot_tmpdir/scmroot/openvdb'...
$ git fetch origin b0daecbfdd3106701b333d7fa7917e450f63d5a2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/openvdb
 * [new ref]         b0daecbfdd3106701b333d7fa7917e450f63d5a2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b0daecb i686 no longer builds due to 4GB memory per thread limitation on 32bit arches.