Tale as old as the world - there's an ABI mismatch: https://github.com/rust-lang/compiler-builtins/pull/527 Fortunately, newest GCCs (from v11, it seems) actually provide most of those intrinsics (even for f64!), so that's pretty cool. (the only intrinsics not provided by GCC are `__powisf2` & `__powidf2`, but our codegen for AVR doesn't emit those anyway.) Fixes https://github.com/rust-lang/rust/issues/118079.