Constant openssl_sys::OPENSSL_BUILT_ON
pub const OPENSSL_BUILT_ON: c_int = 2;
The portability is definied by:
#[cfg(all(any(ossl110, libressl271), not(any())))]
pub const OPENSSL_BUILT_ON: c_int = 2;
#[cfg(all(any(ossl110, libressl271), not(any())))]