SCEst: Allow host types in SLIC compilation

[lken274]

Pre() syntax bugfix:

Calling pre() on an IO signal would translate the pre-variable assignment in tick() as: d->_pA = d->_A;, when it should be d->_pA = d->A;

Allow Host types:

Previously, host types would not be compiled correctly. There was a TODO message saying "SCL doesn't allow anything else then the predefined types", which I think is no longer the case. I would like to use host types, hence, I have done some minimal edits which I hope are correct.

Example working snippet:

#hostcode "#include <mytypes.h>"

module minimal:
type NewType;
function get_some_obj() : NewType;
input A;
output B : NewType;

  present pre(A) then emit B(get_some_obj()) end;
  pause;

end module

Unlike in classic Esterel, I do not think the forward type declaration is actually used here (which is reasonable), but it is syntactically valid.