Add some alignment info where LLVM might otherwise be more pessimistic. In particular, %.nest_arg is always aligned even though it's bitcast from i8*. Pointers in vtables are also guaranteed to be stored at aligned addresses.

module bug7;

class love { }
void bug() {
    love[] child;
    child.length=1;
    assert(child[0] is null);
    child[0]=null;
    assert(child[0] is null);
}
void main()
{
    bug();
}