[ConstraintSystem] Add possibility to mark conjunction element producers as exhausted

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -5886,6 +5886,10 @@ class ConjunctionElementProducer : public BindingProducer<ConjunctionElement> {
   bool needsToComputeNext() const override { return false; }
 
   bool isExhausted() const override { return Index >= Elements.size(); }
+
+  void markExhausted() {
+    Index = Elements.size();
+  }
 };
 
 /// Determine whether given type is a known one