Check equivalencies when calculating range on entry.

Check equivalencies when calculating range on entry.

When propagating on-entry values in the cache, checking if any equivalence
has a known value can improve results.  No new calculations are made.
Only queries via dominators which do not populate the cache are checked.

	PR tree-optimization/106474
	gcc/
	* gimple-range-cache.cc (ranger_cache::fill_block_cache): Query
	range of equivalences that may contribute to the range.

	gcc/testsuite/
	* g++.dg/pr106474.C: New.