$ git clone -n https://src.fedoraproject.org/rpms/gcc.git /var/lib/mock/f42-build-side-1-3589007-46952/root/chroot_tmpdir/scmroot/gcc
Cloning into '/var/lib/mock/f42-build-side-1-3589007-46952/root/chroot_tmpdir/scmroot/gcc'...
$ git fetch origin efcc0e8121a69b3060a3b527e0653fd645c19a0f:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gcc
 * [new ref]         efcc0e8121a69b3060a3b527e0653fd645c19a0f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at efcc0e8 Downstream tests moved to CentOS