vrp: Handle pointers in maybe_set_nonzero_bits [PR108253]

vrp: Handle pointers in maybe_set_nonzero_bits [PR108253]

maybe_set_nonzero_bits calls set_nonzero_bits which asserts that
var doesn't have pointer type.  While we could punt for those
cases, I think we can handle at least some easy cases.
Earlier in maybe_set_nonzero_bits we've checked this is on
(var & cst) == 0
edge and the other edge is __builtin_unreachable, so if cst
is say 3 as in the testcase, we want to turn it into 4 byte alignment
of the pointer.

2023-01-04  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/108253
	* tree-vrp.cc (maybe_set_nonzero_bits): Handle var with pointer
	types.

	* g++.dg/opt/pr108253.C: New test.