Commit 986f361946 started to use
<nix/fetchurl.nix> to "download" the bootstrap binaries from the
Nixpkgs tree, using the file:/// scheme. This has really bad
consequences:
* It makes any derivation depend on the path of the Nixpkgs tree. So
evaluating a package will produce a different .drv file when run
from different locations. No wonder Hydra evaluation has been so
slow lately: for every Nixpkgs evaluation, it had to create tens of
thousands of .drv files, even if nothing had changed.
* It requires the builder to have file system access to the Nixpkgs
tree. So if your tree is in your home directory, the stdenv
bootstrap would probably fail.
So now the binaries are downloaded from tarballs.nixos.org.
Also dropped PowerPC "support".
d4f44d6db3