Use !contains_zero_p for known nonzero tests instead of nonzero_p.

These callers ask whether a range excludes zero, which nonzero_p ()
only approximated (i.e. it is false for e.g. [1, 5]).

Tested on ppc64le Linux.

gcc/ChangeLog:

	* gimple-range-path.cc (path_range_query::adjust_for_non_null_uses):
	Use !contains_zero_p instead of nonzero_p.
	* tree-ssa-structalias.cc (find_what_p_points_to): Likewise.
	* tree-ssanames.cc (set_range_info): Likewise.
	* tree-vrp.cc (execute_ranger_vrp): Likewise.

gcc/analyzer/ChangeLog:

	* region-model.cc (region_model::eval_condition): Likewise.