* nix/libstore/build.cc (canBuildLocally): Allow building armhf-linux builds on aarch64-linux. (DerivationGoal::runChild) Throw error if attempting to build for armhf-linux on an unsupported platform. * doc/guix.texi (Invoking guix build): Document how to build natively for armhf-linux on aarch64-linux. Add note that on some aarch64 machines this is unsupported.