[build] Remove target binary before copy.
[build] Remove target binary before copy.

Fixes #7666. Due to shared mapping of executables Linux doesn't allow
to overwrite binaries that are running; we do as `ocamlopt` and delete
the target file before copy.

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