tree-object-size: Don't let error_mark_node escape for ADDR_EXPR [PR105736]

tree-object-size: Don't let error_mark_node escape for ADDR_EXPR [PR105736]

The addr_expr computation does not check for error_mark_node before
returning the size expression.  This used to work in the constant case
because the conversion to uhwi would end up causing it to return
size_unknown, but that won't work for the dynamic case.

Modify the control flow to explicitly return size_unknown if the offset
computation returns an error_mark_node.

gcc/ChangeLog:

	PR tree-optimization/105736
	* tree-object-size.cc (addr_object_size): Return size_unknown
	when object offset computation returns an error.

gcc/testsuite/ChangeLog:

	PR tree-optimization/105736
	* gcc.dg/builtin-dynamic-object-size-0.c (TV4): New struct.
	(val3): New variable.
	(test_pr105736): New test.
	(main): Call it.

Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org>