* cfg-flags.def (IGNORE): New edge flag.
	* tree-vrp.c (identify_jump_threads): Mark and clear edges
	scheduled for removal with EDGE_IGNORE around call into
	jump threader.  Do no thread across edges with EDGE_IGNORE,
	but do allow threading across those with EDGE_DFS_BACK.

	* gcc.dg/tree-ssa/ssa-dom-thread-7.c: Adjust to look for
	realized jump threads.
	* gcc.dg/tree-ssa-pr66752-3.c: Look in vrp1 dump for jump
	threads rather than dom1 dump.

From-SVN: r229902