vect: Move suggested_unroll_factor applying [PR105940]

vect: Move suggested_unroll_factor applying [PR105940]

As PR105940 shown, when rs6000 port tries to assign
m_suggested_unroll_factor by 4 or so, there will be ICE on:

  exact_div (LOOP_VINFO_VECT_FACTOR (loop_vinfo),
             loop_vinfo->suggested_unroll_factor);

In function vect_analyze_loop_2, the current place of
suggested_unroll_factor applying can't guarantee it's
applied for all cases.  As the case shows, vectorizer
could retry with SLP forced off, the vf is reset by
saved_vectorization_factor which isn't applied with
suggested_unroll_factor before.  It means it can end
up with one vf which neglects suggested_unroll_factor.
I think it's off design, we should move the applying
of suggested_unroll_factor after start_over.

	PR tree-optimization/105940

gcc/ChangeLog:

	* tree-vect-loop.cc (vect_analyze_loop_2): Move the place of
	applying suggested_unroll_factor after start_over.