tree-optimization/113902 - fix VUSE update in move_early_exit_stmts

The following adjusts move_early_exit_stmts to track the last seen
VUSE instead of getting it from the last store which could be a PHI
where gimple_vuse doesn't work.

	PR tree-optimization/113902
	* tree-vect-loop.cc (move_early_exit_stmts): Track
	last_seen_vuse for VUSE updating.

	* gcc.dg/vect/pr113902.c: New testcase.