Track guard/call pair if constrainIfcmpeqne cannot remove guard

If constrainIfcmpeqne cannot call canFoldNonOverriddenGuard because the
target has too many predecessor blocks, the guard/call pair should still
be added to the _callNodeToGuardNodes list.  That allows constrainCall
the opportunity to check whether the guard can be removed after all
the guard blocks have been processed.

Also removed a comment from constrainIfcmpeqne describing an invalid
potential improvement.

compiler/optimizer/VPHandlers.cpp

@@ -9457,18 +9457,19 @@ static TR::Node *constrainIfcmpeqne(OMR::ValuePropagation *vp, TR::Node *node, b
       {
       TR::Node *callNode = node->getVirtualCallNodeForGuard();
 
-      // In order to decide correctly whether the guard can be eliminated, we need to ensure
-      // all predecessor blocks of the call block have been walked, and hence all definitions
-      // used by the call have been considered.  The easiest way to do that is to check
-      // whether the call has only one predecessor - the current block.
-      // A potential refinement would be to check whether all of the call block's predecessors
-      // have been walked, and that this is the last predecessor being visited on this walk.
-      //
       if (callNode &&
-          callNode->getOpCode().isCall() &&
-          target->getPredecessors().size() == 1)
+          callNode->getOpCode().isCall())
          {
-         virtualGuardWillBeEliminated = canFoldNonOverriddenGuard(vp, callNode, node);
+         // In order to decide correctly whether the guard can be eliminated, we need to ensure
+         // all predecessor blocks of the call block have been walked, and hence all definitions
+         // used by the call have been considered.  The easiest way to do that is to check
+         // whether the call has only one predecessor - the current block.
+         //
+         if (target->getPredecessors().size() == 1)
+            {
+            virtualGuardWillBeEliminated = canFoldNonOverriddenGuard(vp, callNode, node);
+            }
+
          if (!virtualGuardWillBeEliminated &&
              vp->lastTimeThrough() &&
              vp->_isGlobalPropagation)