Show build and substitution information when not connected to a TTY
Show build and substitution information when not connected to a TTY

When stderr is not connected to a tty, show "building" and
"substituting" messages, a-la nix-build et al.

Closes https://github.com/NixOS/nix/issues/4402

Co-authored-by: Théophane Hufschmitt <27588844e2c6332bcb160e41403584d835df3d97@users.noreply.github.com>

rycee/nix,rycee/nix,NixOS/nix,rycee/nix,NixOS/nix,NixOS/nix,rycee/nix,NixOS/nix,rycee/nix,NixOS/nix