tree-optimization/111751 - support 1024 bit vector constant reinterpretation

The following ups the limit in fold_view_convert_expr to handle
1024bit vectors as used by GCN and RVV.  It also robustifies
the handling in visit_reference_op_load to properly give up when
constants cannot be re-interpreted.

	PR tree-optimization/111751
	* fold-const.cc (fold_view_convert_expr): Up the buffer size
	to 128 bytes.
	* tree-ssa-sccvn.cc (visit_reference_op_load): Special case
	constants, giving up when re-interpretation to the target type
	fails.