re PR middle-end/86575 (-Wimplicit-fallthrough affects code generation)

Fix PR middle-end/86575

	PR middle-end/86575
	* gimplify.c (collect_fallthrough_labels): Add new argument,
	return location via that, don't modify statements.
	(warn_implicit_fallthrough_r): Adjust call, don't use
	statement location directly.

From-SVN: r266148