tree-optimization/113863 - elide degenerate virtual PHIs when moving ee stores

This makes sure to elide degenerate virtual PHIs when moving stores
across early exits.

	PR tree-optimization/113863
	* tree-vect-data-refs.cc (vect_analyze_early_break_dependences):
	Record crossed virtual PHIs.
	* tree-vect-loop.cc (move_early_exit_stmts): Elide crossed
	virtual PHIs.

	* gcc.dg/vect/pr113863.c: New testcase.