analyzer: fixes to tree_cmp and other comparators

analyzer: fixes to tree_cmp and other comparators

region_model.cc's tree_cmp attempted to verify that the ordering
is symmetric by asserting that
  tree_cmp (x, y) == -tree_cmp (y, x)

This condition is too strong: it's only required for a comparator that
  sign (tree_cmp (x, y)) == -sign (tree_cmp (y, x))
and the incorrect form of the assertion doesn't hold e.g. on s390x where
for certain inputs x, y, tree_cmp (x, y) == 1 and tree_cmp (y, x) == -2,
breaking the build in "make selftest" in stage1.

In any case, these checks are redundant, since qsort_chk performs them.

Additionally, there is a potential lack of transitivity in
worklist::key_t::cmp where hashval_t values are compared by subtraction,
which could fail to be transitive if overflows occur.

This patch eliminates the redundant checks and reimplements the hashval_t
comparisons in terms of < and >, fixing these issues.

gcc/analyzer/ChangeLog:
	* call-string.cc (call_string::cmp_1): Delete, moving body to...
	(call_string::cmp): ...here.
	* call-string.h (call_string::cmp_1): Delete decl.
	* engine.cc (worklist::key_t::cmp_1): Delete, moving body to...
	(worklist::key_t::cmp): ...here.  Implement hash comparisons
	via comparison rather than subtraction to avoid overflow issues.
	* exploded-graph.h (worklist::key_t::cmp_1): Delete decl.
	* region-model.cc (tree_cmp): Eliminate buggy checking for
	symmetry.