Add sodium autotools CI build

[nurupo]

Currently we test nacl autotools builds on CI, but it builds just a static libtoxcore.a. Having a sodium autotools build would test both static and shared builds (it builds both), which would help us find issues that appear only during shared library building, like #2009 and #2015.

[iphydf]

We've removed nacl and the autotools build uses sodium now.