tree-optimization/114998 - use-after-free with loop distribution

tree-optimization/114998 - use-after-free with loop distribution

When loop distribution releases a PHI node of the original IL it
can end up clobbering memory that's re-used when it upon releasing
its RDG resets all stmt UIDs back to -1, even those that got released.

The fix is to avoid resetting UIDs based on stmts in the RDG but
instead reset only those still present in the loop.

	PR tree-optimization/114998
	* tree-loop-distribution.cc (free_rdg): Take loop argument.
	Reset UIDs of stmts still in the IL rather than all stmts
	referenced from the RDG.
	(loop_distribution::build_rdg): Pass loop to free_rdg.
	(loop_distribution::distribute_loop): Likewise.
	(loop_distribution::transform_reduction_loop): Likewise.

	* gcc.dg/torture/pr114998.c: New testcase.