Generate a makefile and run the makefilw with:
$ coq_makefile -f _CoqProject -o Makefile && make
To use nix, the purely functional package manager
to automatically setup the correct build environment, run nix-shell at
the folder with default.nix (top-level folder).
bash$ nix-shell
[nix-shell]: coq_makefile -f _CoqProject -o Makefile && make
This should never fail if the nix-shell succeeds.