Flag: Use designated initializers

src/libexpr/common-eval-args.cc

src/libmain/common-args.cc

src/libmain/shared.cc

src/libstore/globals.cc

src/libutil/args.cc

src/libutil/args.hh

src/libutil/config.cc

src/nix/add-to-store.cc

src/nix/build.cc

src/nix/command.cc

src/nix/copy.cc

src/nix/dev-shell.cc

src/nix/hash.cc

src/nix/installables.cc

src/nix/main.cc

src/nix/run.cc

src/nix/search.cc

src/nix/show-derivation.cc

src/nix/sigs.cc

src/nix/upgrade-nix.cc