Merge pull request #519 from proux01/opam

Backport package from opam repo

Author: proux01

coq-hierarchy-builder.opam

@@ -17,6 +17,9 @@ depends: [
   | "coq" {>= "8.20" & < "8.21~"} & "coq-elpi" {>= "2.4" | = "dev"}
   | "rocq-core" {>= "9.0" | = "dev"} & "coq-elpi" {>= "2.4" | = "dev"})
 ]
+depexts: [
+  [ "wdiff" ] {os-family = "debian" & with-test}
+]
 conflicts: [ "coq-hierarchy-builder-shim" ]
 synopsis: "High level commands to declare and evolve a hierarchy based on packed classes"
 description: """