Fix configure crash on some version strings of camlp5, e.g. "6.18-exp" (bug #5307).
Fix configure crash on some version strings of camlp5, e.g. "6.18-exp" (bug #5307).

ppedrot/coq,ejgallego/coq,Ptival/coq,ppedrot/coq,Matafou/coq,silene/coq,ppedrot/coq,SkySkimmer/coq,coq/coq,Zimmi48/coq,JasonGross/coq,JasonGross/coq,ppedrot/coq,ppedrot/coq,letouzey/coq-wip,maximedenes/coq,maximedenes/coq,Zimmi48/coq,maximedenes/coq,william-lawvere/coq,silene/coq,maximedenes/coq,Lionel-Rieg/coq,Zimmi48/coq,letouzey/coq-wip,letouzey/coq-wip,SkySkimmer/coq,Zimmi48/coq,william-lawvere/coq,gares/coq,coq/coq,JasonGross/coq,letouzey/coq-wip,amintimany/coq,JasonGross/coq,ejgallego/coq,Lionel-Rieg/coq,Matafou/coq,SkySkimmer/coq,Ptival/coq,william-lawvere/coq,gares/coq,gares/coq,coq/coq,maximedenes/coq,ejgallego/coq,letouzey/coq-wip,coq/coq,ejgallego/coq,amintimany/coq,Matafou/coq,gares/coq,amintimany/coq,silene/coq,Lionel-Rieg/coq,Ptival/coq,gares/coq,SkySkimmer/coq