tree-optimization/113831 - wrong VN with structurally identical ref

When we use get_ref_base_and_extent during VN and that ends up using
global ranges to restrict the range of a ref we have to take care
of not using the same expression in the hashtable as for a ref that
could not use that global range.  The following attempts to ensure
this by applying similar logic as get_ref_base_and_extent to
copy_reference_ops_from_ref so they behave consistent.

	PR tree-optimization/113831
	PR tree-optimization/108355
	* tree-ssa-sccvn.cc (copy_reference_ops_from_ref): When
	we see variable array indices and get_ref_base_and_extent
	can resolve those to constants fix up the ops to constants
	as well.
	(ao_ref_init_from_vn_reference): Use 'off' member for
	ARRAY_REF and ARRAY_RANGE_REF instead of recomputing it.
	(valueize_refs_1): Also fixup 'off' of ARRAY_RANGE_REF.

	* gcc.dg/torture/pr113831.c: New testcase.
	* gcc.dg/tree-ssa/ssa-fre-104.c: Likewise.