This option controls whether Rust uses the spec-compliant C ABI when compiling for the wasm32-unknown-unknown target.

This makes it possible to be ABI-compatible with all other spec-compliant Wasm like Rusts wasm32-wasi.

This compiler flag is perma-unstable, as it will be enabled by default in the future with no option to fall back to the old non-spec-compliant ABI.