Our coreutils now uses single-binary-build mode where, by default,
simple shebang scripts are used for all the binaries. That doesn't work
e.g. with the Linux unpacker which only handles standard binaries and
symlinks. Let's use the symlinked mode instead for boostrapping.
This does NOT change any stdenv hashes.
I only tested the case most important to me:
$ nix-build pkgs/top-level/release.nix -A stdenvBootstrapTools.x86_64-linux.test
Several places in the tree associate the ARMv7 system
with the beaglebone platform. Change them to point to
armv7l-hf-multiplatform as it supports several boards (including the
beaglebone as well)
