Function type_builtin_fn 

pub fn type_builtin_fn(
    name: &str,
    tplt: Option<&[TpltParam]>,
    args: &[Type],
) -> Result<Option<Type>, Error>

Compute the return type of calling a built-in function.

The arguments must be loaded.

Does not include constructor built-ins, see type_ctor.

Some functions are still TODO, see call for the list of functions and statuses.