[configure] fix detection of `md5sum`
[configure] fix detection of `md5sum`

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