Fixed ModuleInfo generation to no longer use the ModuleInfo class' default initializer for types/defaults, it's unsafe as initializers don't necesarily match the "formal" type. There might be explicit padding. Changed -g switch to emit DW_LANG_D debug info, make demangling work with a patched GDB, still more work to do for full support of D's Dwarf extensions. Added getNullValue helper method.

module union2;

union U
{
    float f;
    long l;
}

U u;

void main()
{
    assert(u.f !<>= 0);
    {
        uint* p = 1 + cast(uint*)&u;
        {assert(*p == 0);}
    }
}