New early __builtin_unreachable processing.

in VRP passes before __builtin_unreachable MUST be removed, only remove it
if all exports affected by the unreachable can have global values updated, and
do not involve loads from memory.

	PR tree-optimization/110080
	PR tree-optimization/110249
	gcc/
	* tree-vrp.cc (remove_unreachable::final_p): New.
	(remove_unreachable::maybe_register): Rename from
	maybe_register_block and call early or final routine.
	(fully_replaceable): New.
	(remove_unreachable::handle_early): New.
	(remove_unreachable::remove_and_update_globals): Remove
	non-final processing.
	(rvrp_folder::rvrp_folder): Add final flag to constructor.
	(rvrp_folder::post_fold_bb): Remove unreachable registration.
	(rvrp_folder::pre_fold_stmt): Move unreachable processing to here.
	(execute_ranger_vrp): Adjust some call parameters.

	gcc/testsuite/
	* g++.dg/pr110249.C: New.
	* gcc.dg/pr110080.c: New.
	* gcc.dg/pr93917.c: Adjust.