Adds camlp4

Camlp4 is a software system for writing extensible parsers for
programming languages.

Camlp4 was part of the official OCaml distribution until its version
4.01.0.

Homepage: https://github.com/ocaml/camlp4
Fixes ocamlgraph (depends on camlp4) and prooftree (not ready for
OCaml4.02)
Fixes coccinelle (depends on camlp4)
Merge pull request #4215 from vbgl/camlp4

Adds camlp4