fix ppx test for if%lwt
fix ppx test for if%lwt

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