Enable for Coq 8.14 Use default version of OCaml (instead of 4.05) VST is not ready for CompCert 3.10, so it still uses 3.9
* compcert: preparation to move in coqPackages * compcert: move into coqPackages * compcert: remove version 3.7 As a consequence, also remove VST version 2.6 These were broken.