[opam] adds dune dependencies and ignore local switch

.gitignore

@@ -23,7 +23,7 @@ frama_c_journal.ml
 /headers/hdrck
 
 #build
-
+/_opam/
 configure
 autom4te.cache
 .log.autoconf

opam/opam

@@ -106,6 +106,10 @@ run-test: [
 
 depends: [
   "ocaml" { >= "4.08.1" }
+  "dune" { >= "2.8.2" }
+  "dune-configurator"
+  "dune-private-libs"
+  "dune-site"
   "ocamlgraph" { >= "1.8.8" }
   "ocamlfind" # needed beyond build stage, used by -load-module
   "zarith"
@@ -119,6 +123,7 @@ depends: [
   "yojson"
   "why3" { >= "1.3.3" }
   "conf-time" { with-test }
+  "ppx_deriving_yojson"
 ]
 
 depopts: [
@@ -129,8 +134,6 @@ depopts: [
   "mlgmpidl"
   "apron"
   "zmq"
-  "ppx_deriving"
-  "ppx_deriving_yojson"
 ]
 
 messages: [