Fix VarDecls for tuples. Closes #99. I've implemented it this way since it doesn't require any changes in the frontend. However, I think having TypeTuple expressed as LLVM struct types would make much more sense and open the door to tuple lvalues.

module bug39;

struct S
{
    long l;
}

void main()
{
    S s;
    s.l = 23;
    void* p = &s;
}