[IUO] Add a locator for the result of a cast to an IUO type.

Not used yet, so NFC.

lib/Sema/ConstraintLocator.cpp

@@ -78,6 +78,7 @@ void ConstraintLocator::Profile(llvm::FoldingSetNodeID &id, Expr *anchor,
     case KeyPathComponent:
     case ConditionalRequirement:
     case TypeParameterRequirement:
+    case ImplicitlyUnwrappedCoercionResult:
       if (unsigned numValues = numNumericValuesInPathElement(elt.getKind())) {
         id.AddInteger(elt.getValue());
         if (numValues > 1)
@@ -248,6 +249,10 @@ void ConstraintLocator::dump(SourceManager *sm, raw_ostream &out) {
     case TypeParameterRequirement:
       out << "type parameter requirement #" << llvm::utostr(elt.getValue());
       break;
+
+    case ImplicitlyUnwrappedCoercionResult:
+      out << "implictly unwrapped coercion result";
+      break;
     }
   }