set location for src_builtins to //builtin
#288
Opened by flokli at
Observed in Nix error messages, it seems the source code for builtin.derivation is presented as being in //builtin/derivation.nix.
It might make sense to follow the same naming pattern (well, and in our case we might even be able to make the source available in error traces).
I'm not entirely sure yet if the same logic should be applied to the corepkgs hack or not.