middle-end/103271 - avoid VLA init of register

middle-end/103271 - avoid VLA init of register

This avoids using VLA types to initalize a register with
-ftrivial-auto-var-init in some cases.

2021-12-02  Richard Biener  <rguenther@suse.de>

	PR middle-end/103271
	* internal-fn.c (expand_DEFERRED_INIT): When the base
	of the LHS is a decl with matching constant size use
	that as the initialization target instead of an
	eventual VLA typed one.