OCaml 4.05.0 support - cannot build in Homebrew

[ilovezfs]

Following the upgrade to OCaml 4.05.0 in Homebrew, corectl can no longer build.

The error is

==> opam install uri ocamlfind qcow-format conf-libev io-page<2
The following dependencies couldn't be met:
  - qcow-format -> ppx_deriving
  - qcow-format -> sexplib < 113.24.00
Your request can't be satisfied:
  - ppx_deriving is not available because your system doesn't comply with ocaml-version >= "4.02.1" & ocaml-version < "4.05" & opam-version >= "1.2".
  - sexplib<113.01.00 is not available because your system doesn't comply with ocaml-version >= "4.02.1" & ocaml-version < "4.03".
  - sexplib<113.24.00 is not available because your system doesn't comply with ocaml-version >= "4.02.1" & ocaml-version < "4.03".

No solution found, exiting

See
Homebrew/homebrew-core#15681
Homebrew/homebrew-core#15674

CC @AntonioMeireles