remove all files to get a clean branch, then checkout each file
individually from the upstream tag:

  rm -r *

  git fetch origin +refs/tags/libXcursor-1.2.0:refs/tags/libXcursor-1.2.0

  for file in git diff --name-status | awk '/^[CDMRTUX]/ {print $2}';
    do git checkout refs/tags/libXcursor-1.2.0 $file;
  done

removes cruft files present in tarball but not in git source