Removing failure of coq_makefile on no arguments.
Removing failure of coq_makefile on no arguments.

Nevertheless making option -o of coq_makefile recommended as discussed
in PR#6040.

This is one way to resolve the inconsistency with the usage which says
that all arguments are optional.

letouzey/coq-wip,SkySkimmer/coq,gares/coq,maximedenes/coq,gares/coq,coq/coq,Zimmi48/coq,ppedrot/coq,ppedrot/coq,ppedrot/coq,maximedenes/coq,Zimmi48/coq,JasonGross/coq,Matafou/coq,coq/coq,silene/coq,maximedenes/coq,letouzey/coq-wip,Matafou/coq,gares/coq,ejgallego/coq,silene/coq,Matafou/coq,ejgallego/coq,maximedenes/coq,ejgallego/coq,maximedenes/coq,SkySkimmer/coq,coq/coq,ppedrot/coq,ppedrot/coq,ejgallego/coq,letouzey/coq-wip,silene/coq,letouzey/coq-wip,gares/coq,SkySkimmer/coq,letouzey/coq-wip,gares/coq,JasonGross/coq,coq/coq,Zimmi48/coq,Zimmi48/coq,JasonGross/coq,SkySkimmer/coq,JasonGross/coq