Similar to legacy/trac#25368, we can once again expand upon which Rust types are safe to send over the FFI boundary without conversion/serialisation/translation, because Rust's `bool` type and C99's `bool` type are directly compatible. (I think this also makes an even larger argument moving forward for using `bool`s in C wherever it makes sense, since otherwise we need to convert between the libc `uint8_t` type and the native `u8` in Rust.)