linux-x86/1.39.0/src/stdlibs/vendor/libc/src/unix/bsd/freebsdlike/dragonfly/errno.rs

// DragonFlyBSD's __error function is declared with "static inline", so it must
// be implemented in the libc crate, as a pointer to a static thread_local.
f! {
    pub fn __error() -> *mut ::c_int {
        &mut errno
    }
}

extern {
    #[thread_local]
    pub static mut errno: ::c_int;
}