[dune] Build coqc.byte executable.
[dune] Build coqc.byte executable.

This may be useful in a few cases, like testing compilation with
byte-plugins; I chose to install it globally tho it is more of a
developer target.

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