Add x86 MSA model + tests

[hernanponcedeleon]

See here

[ThomasHaas]

This is quite an old model from Herd7, right? It certainly doesn't look too nice.
I would guess that changing our com-tso to com-tso;si is all we need to do on our side.

[hernanponcedeleon]

The link is from the companion artifact for the armed-cats paper (2022?).

The model is not the most interesting thing of the link (as you said, we might get away with a simple change to our model as we did for aarch64), the tests are.