Adds explicit alignment information for alloca instructions in general, there's a few cases that still needs to be looked at but this should catch the majority. Fixes ticket #293 .

module structs5;

void main()
{
    {S s = S();}
    {T t = T(1);}
    {U u = U();}
}

struct S
{
}

struct T
{
    int i;
}

struct U
{
    S s;
    long l;
}