$ git clone -n https://src.fedoraproject.org/rpms/libsigc++.git /var/lib/mock/f41-build-1037307-18787/root/chroot_tmpdir/scmroot/libsigc++
Cloning into '/var/lib/mock/f41-build-1037307-18787/root/chroot_tmpdir/scmroot/libsigc++'...
$ git fetch origin 9eecdd3a656f0ec97e8002e57817205e7484a320:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/libsigc++
 * [new ref]         9eecdd3a656f0ec97e8002e57817205e7484a320 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 9eecdd3 Eliminate use of obsolete %patchN syntax (#2283636)