$ git clone -n https://src.fedoraproject.org/rpms/rust-cxx.git /var/lib/mock/f45-build-41128-779/root/chroot_tmpdir/scmroot/rust-cxx
Cloning into '/var/lib/mock/f45-build-41128-779/root/chroot_tmpdir/scmroot/rust-cxx'...
$ git fetch origin 6d9b7ccac6bf60fac5800c5706a35b8ea5605ea1:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-cxx
 * [new ref]         6d9b7ccac6bf60fac5800c5706a35b8ea5605ea1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 6d9b7cc Update to version 1.0.200; Fixes RHBZ#2528930