tree-optimization/111950 - vectorizer loop copying

tree-optimization/111950 - vectorizer loop copying

The following simplifies LC-PHI arg population during epilog peeling,
thereby fixing the testcase in this PR.

	PR tree-optimization/111950
	* tree-vect-loop-manip.cc (slpeel_duplicate_current_defs_from_edges):
	Remove.
	(find_guard_arg): Likewise.
	(slpeel_update_phi_nodes_for_guard2): Likewise.
	(slpeel_tree_duplicate_loop_to_edge_cfg): Remove calls to
	slpeel_duplicate_current_defs_from_edges, do not elide
	LC-PHIs for invariant values.
	(vect_do_peeling): Materialize PHI arguments for the edge
	around the epilog from the PHI defs of the main loop exit.

	* gcc.dg/torture/pr111950.c: New testcase.