PR fortran/50408
* trans-decl.c (gfc_get_module_backend_decl): Also copy
ts.u.derived from the gsym if the ts.type is BT_CLASS.
(gfc_get_extern_function_decl): Copy also the backend_decl
for the symbol's ts.u.{derived,cl} from the gsym.
* trans-types.c (gfc_copy_dt_decls_ifequal): Directly
return if "from" and "to" are the same.