I think that “unix” or “windows” feature of cfg is usually defined automatically by rustc.
Can I define them by myself?
Here is a background.
I am making wasm in Rust code. My library depends the crate “aligned_alloc” and it describes some module for both “unix” feature and “windows” feature.
Since wasm is neither “unix” nor “windows”, I got an error “Use of undeclared type or module”.
It may work if “unix”, because aligned_alloc uses libc in this case and there is a library for libc in wasm.
I saw explanations of features section in Cargo.toml, but it seems for creating new features, not for adding existing features.