tree-optimization/114832 - wrong dominator info with vect peeling

When we update the dominator of the redirected exit after peeling
we check whether the immediate dominator was the loop header rather
than the exit source when we later want to just update it to the
new source.  The following fixes this oversight.

	PR tree-optimization/114832
	* tree-vect-loop-manip.cc (slpeel_tree_duplicate_loop_to_edge_cfg):
	Fix dominance check.

	* gcc.dg/vect/pr114832.c: New testcase.