middle-end/102269 - avoid auto-init of empty types

This avoids initializing empty types for which we'll eventually
leave a .DEFERRED_INIT call without a LHS.

2021-09-10  Richard Biener  <rguenther@suse.de>

	PR middle-end/102269
	* gimplify.c (is_var_need_auto_init): Empty types do not need
	initialization.

	* gcc.dg/pr102269.c: New testcase.