respect print-missing variable in new-style build command
respect print-missing variable in new-style build command

Currently nix-build prints the "printMissing" information by default,
nix build doesn’t.
People generally don‘t notice this because the standard log-format of
nix build would not display the printMissing
output long enough to perceive the information.

This addresses https://github.com/NixOS/nix/issues/6561

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