re PR c/41935 (ICE : tree check: expected integer_cst, have nop_expr in int_cst_value, at tree.c:8301)

	PR middle-end/41935
	* c-common.c (fold_offsetof_1) <case ARRAY_REF>: Don't crash for VLAs
	or non-constant index, allow index one past the last element and
	allow exceeding array bound in arrays that might be used as flexible
	array members.

	* gcc.dg/pr41935.c: New test.
	* c-c++-common/pr41935.c: New test.
	* c-c++-common/builtin-offsetof.c (f0): Allow index one past the last
	element.
	* gcc.c-torture/execute/pr41935.c: New test.

From-SVN: r153962