Ensure PHI equivalencies do not dominate the argument edge.

Ensure PHI equivalencies do not dominate the argument edge.

When we create an equivalency between a PHI definition and an argument,
ensure the definition does not dominate the incoming argument edge.

	PR tree-optimization/108139
	PR tree-optimization/109462
	* gimple-range-cache.cc (ranger_cache::fill_block_cache): Remove
	equivalency check for PHI nodes.
	* gimple-range-fold.cc (fold_using_range::range_of_phi): Ensure def
	does not dominate single-arg equivalency edges.