tree-optimization/107803 - abnormal cleanup from the SSA propagator

The SSA propagator is missing abnormal cleanup which shows in a
sanity check in the uninit engine (and missed CFG verification).
The following adds that.

	PR tree-optimization/107803
	* tree-ssa-propagate.cc (substitute_and_fold_dom_walker): Add
	need_ab_cleanup member.
	(substitute_and_fold_dom_walker::before_dom_children): When
	a stmt can no longer transfer control flow abnormally set
	need_ab_cleanup.
	(substitute_and_fold_engine::substitute_and_fold): Cleanup
	abnormal control flow.

	* g++.dg/pr107803.C: New testcase.