Removed some checks for abstract llvm types that were too strict, a 'opaque* null' is a valid initializer... when structs in D can be just a forward reference.

extern(C) void gc_collect();

class C
{
  int i = 42;
}

C data;

void main()
{
  data = new C;
  gc_collect();
  assert(data.i == 42);
}