nix-build: Ignore --indirect
nix-build: Ignore --indirect

Note that nix-build always creates indirect roots.

Fixes #1830.

peti/nix,dtzWill/nix,shlevy/nix,dtzWill/nix,layus/nix,zimbatm/nix,dezgeg/nix,dezgeg/nix,ehmry/nix,dtzWill/nix,rycee/nix,peti/nix,pikajude/nix,dezgeg/nix,NixOS/nix,zimbatm/nix,zimbatm/nix,rycee/nix,dezgeg/nix,dtzWill/nix,peti/nix,layus/nix,layus/nix,ehmry/nix,ehmry/nix,shlevy/nix,dtzWill/nix,shlevy/nix,vcunat/nix,zimbatm/nix,dezgeg/nix,rycee/nix,pikajude/nix,NixOS/nix,ehmry/nix,peti/nix,NixOS/nix,NixOS/nix,pikajude/nix,vcunat/nix,vcunat/nix,rycee/nix,rycee/nix,layus/nix,NixOS/nix,layus/nix,vcunat/nix,ehmry/nix,shlevy/nix,peti/nix,shlevy/nix,ehmry/nix