re PR tree-optimization/92691 (ICE in strlen_dom_walker::before_dom_children at gcc/tree-ssa-strlen.c:5177 since r274933)

	PR tree-optimization/92691
	* tree-ssa-strlen.c (handle_store): Clarify return value meaning
	in function comment.
	(strlen_check_and_optimize_call): Likewise.  For handle_printf_call
	calls, return !handle_printf_call rather than always returning true.
	(check_and_optimize_stmt): Describe return value meaning in function
	comment.  Formatting fix.

	* gcc.dg/tree-ssa/builtin-snprintf-10.c: New test.

From-SVN: r278803