[groff] Merge conflict for "gnulib"

[Bjarni Ingi Gislason]

  Output form "git pull origin master":

>From git://git.savannah.gnu.org/groff
 * branch              master     -> FETCH_HEAD
warning: Failed to merge submodule gnulib (commits don't follow merge-base)
Auto-merging gnulib
CONFLICT (submodule): Merge conflict in gnulib
Auto-merging contrib/mom/om.tmac-u
Removing VERSION
Removing REVISION
Auto-merging ChangeLog
Auto-merging .gitignore
Automatic merge failed; fix conflicts and then commit the result.

  Output from "git ls-files -u":

160000 e70694158bc1da629241f24757076278aa60a356 1       gnulib
160000 4084b3a1094372b960ce4a97634e08f4538c8bdd 2       gnulib
160000 cf56f8f618c48cfadd2499ced58574633d12f129 3       gnulib


  How is the conflict to be resolved, "git diff --check" gives no
output?