Fix log-prefix of `nix build -L`
Fix log-prefix of `nix build -L`

Alternative fix to #3661. The cause was that 'name' is a
std::string_view into a temporary which could get overwritten.

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