Enable solve_ndisj to solve `∅ ⊆ X`.

opam.pins

-coq-stdpp https://gitlab.mpi-sws.org/robbertkrebbers/coq-stdpp 36363712499dbdf7a4cd2acf91877787b839c79a
+coq-stdpp https://gitlab.mpi-sws.org/robbertkrebbers/coq-stdpp fd8a6717a2610c00dec920ee5f33b00b14ef1fbf

theories/base_logic/lib/namespaces.v

@@ -93,6 +93,7 @@ Hint Extern 0 (_ ⊥ _) => apply ndot_ne_disjoint; congruence : ndisj.
 Hint Resolve ndot_preserve_disjoint_l ndot_preserve_disjoint_r
      nclose_subseteq' ndisj_difference_l : ndisj.
 Hint Resolve namespace_subseteq_difference_l | 100 : ndisj.
+Hint Resolve (empty_subseteq (A:=positive) (C:=coPset)) : ndisj.
 
 Ltac solve_ndisj :=
   repeat match goal with