[ConstraintSystem] Integrate emergency break into iterative solver loop

There are situations when solver goes exponential, before
(when solver was recursive) it would fail relatively quickly by running
out of stack space, now we really need to make sure that emergency
break is in place in main solver loop, otherwise we risk it running for
a really long time if doesn't consume too much memory since default
timeout is ~10 mins.

Author: xedin

lib/Sema/CSStep.cpp

@@ -249,7 +249,7 @@ bool SplitterStep::mergePartialSolutions() const {
 StepResult ComponentStep::take(bool prevFailed) {
   // One of the previous components created by "split"
   // failed, it means that we can't solve this component.
-  if (prevFailed)
+  if (prevFailed || CS.getExpressionTooComplex(Solutions))
     return done(/*isSuccess=*/false);
 
   if (!IsSingle && CS.TC.getLangOpts().DebugConstraintSolver) {