Constant openssl_sys::OPENSSL_PLATFORM
pub const OPENSSL_PLATFORM: c_int = 3;
The portability is definied by:
#[cfg(all(any(ossl110, libressl271), not(any())))]
pub const OPENSSL_PLATFORM: c_int = 3;
#[cfg(all(any(ossl110, libressl271), not(any())))]