A library declared with `(wrapped (transition "..."))` exposes each
public module under two names: the wrapped form (e.g. `Mylib.Foo`)
and a bare-name compat shim (e.g. `Foo`). The shim lets downstream
code keep using the bare name during migration; any reference to it
raises a deprecation alert carrying the library's transition message.

Without alert silencing, a consumer that reaches for the bare name
fails to build:

  $ dune build 2>&1 | grep -v ocamlc
  File "fooexe.ml", line 3, characters 0-3:
  3 | Bar.run ();;
      ^^^
  Error (alert deprecated): module Bar
  Will be removed past 2020-20-20. Use Mylib.Bar instead.
  
  File "fooexe.ml", line 4, characters 0-3:
  4 | Foo.run ();;
      ^^^
  Error (alert deprecated): module Foo
  Will be removed past 2020-20-20. Use Mylib.Foo instead.
  
  File "fooexe.ml", line 7, characters 11-20:
  7 | module X : Intf_only.S = struct end
                 ^^^^^^^^^
  Error (alert deprecated): module Intf_only
  Will be removed past 2020-20-20. Use Mylib.Intf_only instead.
  [1]

Silencing `-alert -deprecated` on the consumer lets the migration
proceed: the consumer builds, reaching the bare-name compat shims
and thereby the library's internal modules.

  $ rm dune
  $ cat > dune <<EOF
  > (executable
  >  (name fooexe)
  >  (libraries mylib)
  >  (flags (:standard -alert -deprecated)))
  > EOF
  $ dune build
