[gitlab] Do expensive builds with a flambda-compiled Coq.
[gitlab] Do expensive builds with a flambda-compiled Coq.

Gains seem superior to 50%, but data is taken from Gitlab so no
reliable at all.

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