In chroot builds, allow paths in chroot different than in /

[viric]

With a syntax in nix.conf allowing lines like:
build-chroot-dirs = /bin=/mystatic/bin

this would allow to avoid having to include /bin and /lib into the chroot of the builds. I think most people expect the chroot builds to allow getting rid of /lib and /bin in the builds.

In that example, /mystatic/bin could include a single statically built 'sh', and that should be enough to run a build in a system where nixpkgs has a pure stdenv, without any base-system files in the chroot.

[shlevy]

+1