fix compilation with ocaml < 4
fix compilation with ocaml < 4

pirapira/coq2rust,silene/coq,gares/coq,ppedrot/coq,TOSPIO/coq,gmalecha/coq,gmalecha/coq,barras/coq,Zimmi48/coq,coq/coq,Lionel-Rieg/coq,Matafou/coq,jpdeplaix/coq,asr/coq,letouzey/coq-wip,mlasson/coq,maximedenes/coq,TheTypoMaster/coq,ejgallego/coq,Lionel-Rieg/coq,coq/coq,Ptival/coq,TOSPIO/coq,8l/coq,amintimany/coq,TheTypoMaster/coq,TOSPIO/coq,barras/coq,JasonGross/coq,Lionel-Rieg/coq,JasonGross/coq,Matafou/coq,8l/coq,asr/coq,ppedrot/coq,SkySkimmer/coq,gares/coq,william-lawvere/coq,gares/coq,maximedenes/coq,mlasson/coq,mattam82/coq,ale-f/coq,pirapira/coq2rust,Ptival/coq,mattam82/coq,jpdeplaix/coq,8l/coq,letouzey/coq-wip,letouzey/coq-wip,aspiwack/coq,ale-f/coq,silene/coq,aspiwack/coq,Zimmi48/coq,Zimmi48/coq,maximedenes/coq,gares/coq,Matafou/coq,herbelin/github-coq,maximedenes/coq,Zimmi48/coq,ejgallego/coq,SkySkimmer/coq,jpdeplaix/coq,mlasson/coq,ppedrot/coq,coq/coq,amintimany/coq,TheTypoMaster/coq,mattam82/coq,SkySkimmer/coq,william-lawvere/coq,herbelin/github-coq,maximedenes/coq,JasonGross/coq,william-lawvere/coq,JasonGross/coq,amintimany/coq,Ptival/coq,pirapira/coq2rust,asr/coq,shindere/coq,ppedrot/coq,silene/coq,shindere/coq,letouzey/coq-wip,aspiwack/coq,ppedrot/coq,ejgallego/coq,shindere/coq,letouzey/coq-wip,SkySkimmer/coq,ale-f/coq,gares/coq,herbelin/github-coq,ejgallego/coq,gmalecha/coq,coq/coq,barras/coq