gimple-ssa-sprintf.c (try_substitute_return_value): Remove info.nowrite calls with no lhs that can't throw.

	* gimple-ssa-sprintf.c (try_substitute_return_value): Remove
	info.nowrite calls with no lhs that can't throw.  Return bool
	whether gsi_remove has been called or not.
	(pass_sprintf_length::handle_gimple_call): Return bool whether
	try_substitute_return_value called gsi_remove.  Formatting fix.
	(pass_sprintf_length::execute): Don't use gsi_remove if
	handle_gimple_call returned true.

	* gcc.dg/tree-ssa/builtin-snprintf-1.c: New test.

From-SVN: r244384