tree-optimization/106131 - wrong code with FRE rewriting

tree-optimization/106131 - wrong code with FRE rewriting

The following makes sure to not use the original TBAA type for
looking up a value across an aggregate copy when we had to offset
the read.

2022-06-30  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/106131
	* tree-ssa-sccvn.cc (vn_reference_lookup_3): Force alias-set
	zero when offsetting the read looking through an aggregate
	copy.

	* g++.dg/torture/pr106131.C: New testcase.

(cherry picked from commit 9701432ff79926a5dd3303be3417e0bd0c24140b)