Travis: build Camlp4 syntax during strict build
Travis: build Camlp4 syntax during strict build

[skip appveyor]

rneswold/lwt,rneswold/lwt,ocsigen/lwt,c-cube/lwt,c-cube/lwt,rneswold/lwt,ocsigen/lwt,ocsigen/lwt,c-cube/lwt