Re: [PATCH v2 2/4] uaccess: always export _copy_[from|to]_user with CONFIG_RUST

[Valentin Obst]

> -#else
>  extern __must_check unsigned long
>  _copy_from_user(void *, const void __user *, unsigned long);
> -#endif

This function is now unconditionally declared, but only defined if
`!defined(INLINE_COPY_FROM_USER) || defined(CONFIG_RUST)`, i.e., in the
common case where it is inlined and Rust is disabled this can lead to
link-time problems if someone decides to use it.