Add Makefile.uk

Add Makefile.uk

In the original build, there are two kinds of sources: for core functionality
and for extensions. Each of them has a different set of compiler flags. In
order to emulate the same behavior, we define two libraries: 'python3-core' and
'python3-extensions'. Please notice that we still keep a 'python3' library as
the main logical library.

Signed-off-by: Vlad-Andrei Badoiu <vlad_andrei.badoiu@stud.acs.upb.ro>
Signed-off-by: Costin Lupu <costin.lupu@cs.pub.ro>
Reviewed-by: Felipe Huici <felipe.huici@neclab.eu>