Apply workaround to iterator comparison bug

This is a workaround to a bug that gets triggered in
dependence_graph.cpp - in the function
dep_graph_domaint::control_dependencies,
find is called on cfg_dominators_templatet::target_sett, with
an iterator parameter called "from".

It is not ensured that this iterator is from the same list
as the iterators within the dominators set, this is a problem
according to C++ Draft Standard N3960:

24.2.1

An iterator j is called reachable from an iterator i if and only if there
is a finite sequence of applications of the expression ++i that makes i == j.
If j is reachable from i, they refer to elements of the same sequence.

24.2.5

The domain of == for forward iterators is that of iterators over the same
underlying sequence.

Author: hannes-steffenhagen-diffblue

src/analyses/cfg_dominators.h

@@ -183,7 +183,19 @@ class dominatorst
 
   const_iterator find(const T &node) const
   {
-    return std::find(begin(), end(), node);
+    std::less<T> less;
+    // FIXME This works around a bug in other parts of the code
+    // in particular, dependence_graph.cpp,
+    // where iterators to different lists than those that are
+    // stored in this set are passed to find.
+    // The Debug libstdc++ will (correctly!) run into an assertion failure
+    // using std::find. std::less for some reason doesn't trigger this assertion
+    // failure, so we use this as an ugly workaround until that code is fixed.
+
+    // NOLINTNEXTLINE
+    return std::find_if(cbegin(), cend(), [&](const T &other_node) {
+      return !less(node, other_node) && !less(other_node, node);
+    });
   }
 
   /// The size of the set; Linear time on the first call,