pkgs: development: Use gcc as default cc instead of clang

$ docker run --rm -it -v $(pwd):/work -w /work registry.cri.epita.fr/cri/infrastructure/nixpie/nixos-pie cc
clang-12: error: no input files

$ docker run --rm -it -v $(pwd):/work -w /work nixos-pie:7bryp3481bzw00bvi0idxxcp66pz3fnz cc
gcc: fatal error: no input files
compilation terminated.