re PR c/82210 (Having _Alignas in a struct with VLAs causes writing to one array to overwrite another)

	PR c/82210
	* stor-layout.c (place_field): For variable length fields, adjust
	offset_align afterwards not just based on the field's alignment,
	but also on the size.

	* gcc.c-torture/execute/pr82210.c: New test.

From-SVN: r257635