This contains the history of this target. Core is built with
cargo build --release -Zbuild-std=core. This checks that
codegen/linking of core works, but does not check whether std builds.
The build is performned with
cargo build --release -Zbuild-std for a library crate. This
checks whether everything builds successfully (excluding binary linking,
which often requires complex toolchains). For no-std targets, Cargo's
build-std logic is used for figuring out whether to build std or not. On
older targets (older than November 2024) this does not always work
reliably, so some failed std builds there are simply no-std targets.