This is done by introducing a new new_global_entity() function for
constructing globals/adding a visibility argument to new_alias_entity().

One Conv is sufficient.

The modes did not match in several places.

Simplify the creation of instrinsic/runtime function entities a bit and avoid creating duplicate types.

* No \n at end; panic() adds one
* No punctuation mark at end
* Lowercase first letter

You can simply build a Add(Mul,...) pattern now as codeselection will match
this to an Mla now.