Fix missing static declaration.

src/xt_redist.c

@@ -184,7 +184,7 @@ xt_redist_check_comms(Xt_redist *redists, int num_redists, MPI_Comm comm) {
   }
 }
 
-size_t
+static size_t
 xt_ranks_uniq_count(size_t num_rank_sets,
                     const size_t *restrict num_ranks,
                     const int *const ranks[num_rank_sets])