d: Fix FAIL in gdc.dg/runnable.d on X32 targets (PR94609)

Patch fixes test failure seen on X32 where a nested struct was passed in
registers, rather than via invisible reference.  Now, all non-POD
structs are passed by invisible reference, not just those with a
user-defined copy constructor/destructor.

gcc/d/ChangeLog:

	PR d/94609
	* d-codegen.cc (argument_reference_p): Don't check TREE_ADDRESSABLE.
	(type_passed_as): Build reference type if TREE_ADDRESSABLE.
	* d-convert.cc (convert_for_argument): Build explicit TARGET_EXPR if
	needed for arguments passed by invisible reference.
	* types.cc (TypeVisitor::visit (TypeStruct *)): Mark all structs that
	are not POD as TREE_ADDRESSABLE.