re PR tree-optimization/17806 (compiler error: in verify_loop_structure, at cfgloop.c:1491 , works -O2, breaks with -O3)

	PR tree-optimization/17806
	* cfghooks.c (split_edge): Update IRREDUCIBLE_LOOP flags.
	* cfgloopmanip.c (loop_split_edge_with): Updating of IRREDUCIBLE_LOOP
	flags moved to split_edge.

From-SVN: r88665