middle-end: Fix dominators updates when peeling with multiple exits [PR113144]

When we peel at_exit we are moving the new loop at the exit of the previous
loop.  This means that the blocks outside the loop dat the previous loop used to
dominate are no longer being dominated by it.

The new dominators however are hard to predict since if the loop has multiple
exits and all the exits are an "early" one then we always execute the scalar
loop.  In this case the scalar loop can completely dominate the new loop.

If we later have skip_vector then there's an additional skip edge added that
might change the dominators.

The previous patch would force an update of all blocks reachable from the new
exits.  This one updates *only* blocks that we know the scalar exits dominated.

For the examples this reduces the blocks to update from 18 to 3.

gcc/ChangeLog:

	PR tree-optimization/113144
	PR tree-optimization/113145
	* tree-vect-loop-manip.cc (slpeel_tree_duplicate_loop_to_edge_cfg):
	Update all BB that the original exits dominated.

gcc/testsuite/ChangeLog:

	PR tree-optimization/113144
	PR tree-optimization/113145
	* gcc.dg/vect/vect-early-break_94-pr113144.c: New test.