fix and reject warnings on Coq 8.13

.gitlab-ci.yml

@@ -38,6 +38,7 @@ build-coq.8.13.0:
   <<: *template
   variables:
     OPAM_PINS: "coq version 8.13.0"
+    DENY_WARNINGS: "1"
 
 build-coq.8.12.2:
   <<: *template

Makefile.coq.local

@@ -15,7 +15,7 @@ test: $(TESTFILES:.v=.vo)
 # Make sure everything imports the options, and all Instance/Argument/Hint are qualified.
 	$(HIDE)for FILE in $(VFILES); do \
 	  if ! fgrep -q 'From stdpp Require Import options.' "$$FILE"; then echo "ERROR: $$FILE does not import 'options'."; echo; exit 1; fi ; \
-	  if egrep '^\s*(Instance|Arguments|Hint (Extern|Constructors|Resolve|Immediate|Mode|Opaque|Transparent|Unfold))\s' "$$FILE"; then echo "ERROR: $$FILE contains unqualified 'Instance'/'Arguments'/'Hint'."; echo; exit 1; fi \
+	  if egrep '^\s*(Instance|Arguments|Remove|Hint (Extern|Constructors|Resolve|Immediate|Mode|Opaque|Transparent|Unfold))\s' "$$FILE"; then echo "ERROR: $$FILE contains unqualified 'Instance'/'Arguments'/'Hint'."; echo; exit 1; fi \
 	done
 .PHONY: test
 

theories/list.v

@@ -31,7 +31,7 @@ Instance: Params (@drop) 1 := {}.
 
 Global Arguments Permutation {_} _ _ : assert.
 Global Arguments Forall_cons {_} _ _ _ _ _ : assert.
-Remove Hints Permutation_cons : typeclass_instances.
+Global Remove Hints Permutation_cons : typeclass_instances.
 
 Notation "(::)" := cons (only parsing) : list_scope.
 Notation "( x ::.)" := (cons x) (only parsing) : list_scope.