`FuncPtr` mapping: support empty-paren functions and varargs

[ForNeVeR]

#356 introduced mapping of function pointer types to FuncPtr<TDelegate>.

Currently, there's no mapping for functions with empty parens or functions with vararg parameters.

We should support that.

While implementing, see number 487 in the project code. There are several places where the changes will be required.

This is important for us to support compiling of all C programs in the wide architecture.