tree-optimization/127018 - properly schedule SLP SCCs

I have realized I failed to update the SCC scheduling part for
schedule verification.  So this properly honors the scheduling
result for SCC components and makes sure to set the result
on all components to make it accessible to all possible further
entries to the SCC.

No test coverage yet.

	PR tree-optimization/127018
	* tree-vect-slp.cc (vect_schedule_scc): For SCCs of
	multiple components update the scheduling state and
	propagate it to all nodes.