Fix a heuristic used by legacy typeclass resolution.
Fix a heuristic used by legacy typeclass resolution.

The evarmap used by the heuristic could contain resolved evars, which could
lead to a failure of backtracking in the EConstr branch. This is experimental
and may be to costly.

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