Move storage of final vtbl from BaseClass to IrInterface: BaseClass instances are shared! Always use the target's irstruct interfaceMap when building the const initializer. Tango helloworld works again.

enum
{
    LLVMnone,
    LLVMintrinsic,
    LLVMno_typeinfo,
    LLVMno_moduleinfo,
    LLVMalloca,
    LLVMva_start,
    LLVMva_copy,
    LLVMva_end,
    LLVMva_arg,
    LLVMldc
};