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.

module bug49;

struct S
{
    int i;
    long l;
}

void main()
{
    S s;
    s.i = 0x__FFFF_FF00;
    s.l = 0xFF00FF_FF00;
    s.i &= s.l;
}