tree-optimization/119057 - bogus double reduction detection

tree-optimization/119057 - bogus double reduction detection

We are detecting a cycle as double reduction where the inner loop
cycle has extra out-of-loop uses.  This clashes at least with
assumptions from the SLP discovery code which says the cycle
isn't reachable from another SLP instance.  It also was not intended
to support this case, in fact with GCC 14 we seem to generate wrong
code here.

	PR tree-optimization/119057
	* tree-vect-loop.cc (check_reduction_path): Add argument
	specifying whether we're analyzing the inner loop of a
	double reduction.  Do not allow extra uses outside of the
	double reduction cycle in this case.
	(vect_is_simple_reduction): Adjust.

	* gcc.dg/vect/pr119057.c: New testcase.