tree-optimization/109524 - ICE with VRP edge removal

tree-optimization/109524 - ICE with VRP edge removal

VRP queues edges to process late for updating global ranges for
__builtin_unreachable.  But this interferes with edge removal
from substitute_and_fold.  The following deals with this by
looking up the edge with source/dest block indices which do not
become stale.

	PR tree-optimization/109524
	* tree-vrp.cc (remove_unreachable::m_list): Change to a
	vector of pairs of block indices.
	(remove_unreachable::maybe_register_block): Adjust.
	(remove_unreachable::remove_and_update_globals): Likewise.
	Deal with removed blocks.

	* g++.dg/pr109524.C: New testcase.