Rust has yet to standardize an ABI. Yes you can call or expose a function with C calling conventions. However, you cant pass all native rust types like this, and lose some semantics.
However, as the parent comment you responded to you can enable LTO when compiling C. As rust is mostly always statically linked it basically always got LTO optimizations.
Even with static linking, Rust produces separate compilation units a least at the crate level (and depending on compiler settings, within crates). You won't get LTO between crates if you don't explicitly request it. It does allow inlining across compilation units without LTO, but only for functions explicitly marked as `#[inline]`.
However, as the parent comment you responded to you can enable LTO when compiling C. As rust is mostly always statically linked it basically always got LTO optimizations.