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 typeinfo2;

void main()
{
    auto ti = typeid(float);
    float f = 2.5;
    hash_t fh = ti.getHash(&f);
    assert(ti.next is null);
    float g = 4.0;
    ti.swap(&f,&g);
    assert(f == 4.0 && g == 2.5);
    assert(fh == *cast(uint*)(&g));
    assert(!ti.flags);
}