It's hard to put the sourcing of ./.attrs.sh into all builder
consistently - mistakes will happen. Thus, load structured attrs once in
make-derivation and then source the remaining builder on top.
This should fix quite a few builders with structured attributes in
principle. Most importantly it helps substitute / substituteAll, which
are required for bootstrap on some platforms.
Ensure that archive members are added in sorted order with a fixed
mtime. This allows `nix-build --check` to succeed (when building a
tarball of a simple system configuration).
We also remove env-vars which doesn't appear to do much apart from
capture a bunch of store paths we probably don't want.
This is an alternative to
4b78a5b5fb
