OpenSSL dependency for Rust

[danieldk]

@TheSirC

As stated in my original post, I then integrated my working solution in the relevant part of the wiki.

Thanks for documenting things in the wiki. You shouldn’t have to set OPENSSL_DIR/OPENSSL_LIB_DIR. The openssl-sys build script uses pkgconfig when it is available. So, it should be sufficient to add pkgconfig to your buildInputs,