Fix #5061: Warnings flag has no discernible value
Fix #5061: Warnings flag has no discernible value

The default value of the warnings flag was printed as an empty string,
now replaced by "default".

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