encodings: Build encodings

encodings: Build encodings

All encodings are included in a new library, libruby_enc. Given that the
extensions files are generated at build time by the origin build system, we
also have to run `./configure` and `make` for the original build before
building them for Unikraft. This is done once for both extensions and
encodings.

Signed-off-by: Costin Lupu <costin.lupu@cs.pub.ro>
Reviewed-by: Stefan Teodorescu <stefanl.teodorescu@gmail.com>