$ git clone -n https://src.fedoraproject.org/rpms/glibc.git /var/lib/mock/f40-build-775879-128477/root/chroot_tmpdir/scmroot/glibc
Cloning into '/var/lib/mock/f40-build-775879-128477/root/chroot_tmpdir/scmroot/glibc'...
$ git fetch origin 23dbf2db005fc80d9b95ced7a071f295bc0a241d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/glibc
 * [new ref]         23dbf2db005fc80d9b95ced7a071f295bc0a241d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 23dbf2d Auto-sync with upstream branch master