* coreutils toolchain: Use statically linked linux amd64 variant
Uutils has a musl release artifact for linux amd64.
In the future, it should probably also be possible to add a
aarch64 musl toolchain. At the moment, this is not an upstream release
artifact.
* coreutils toolchain: temporarily add back old darwin variant
On release 0.0.26 of uutils/coreutils, the darwin x86_64 binary is missing.
Also, any releases between 0.0.23 and 0.0.26 are missing binary artifacts.
Downgrade coreutils toolchain on darwin x86_64 for now.
https://github.com/uutils/coreutils/releases/tag/0.0.26
In particular this makes our bazelrc presets more compliant with client codebases, ensuring they can copy these files and not trip on their own pre-commit check
