[Constraint graph] Handle orphaned constraints within connected components

Move the logic for creating connected components of orphaned
constraints into the connected-components algorithm code, rather than
making it a special part of SplitterStep.

lib/Sema/ConstraintGraph.cpp

@@ -540,6 +540,8 @@ namespace {
 
       // Assign each type variable to its appropriate component.
       SmallVector<Component, 1> components;
+      components.reserve(
+          validComponents.size() + cg.getOrphanedConstraints().size());
       llvm::SmallDenseMap<TypeVariableType *, unsigned> componentIdxMap;
       for (auto typeVar : typeVars) {
         // Find the representative. If we aren't creating a type variable
@@ -577,6 +579,12 @@ namespace {
         components[componentIdxMap[rep]].constraints.push_back(&constraint);
       }
 
+      // Gather orphaned constraints; each gets its own component.
+      for (auto orphaned : cg.getOrphanedConstraints()) {
+        components.push_back({ });
+        components.back().constraints.push_back(orphaned);
+      }
+
       return components;
     }
 
@@ -635,7 +643,6 @@ ConstraintGraph::computeConnectedComponents(
   // Perform connected components via a union-find algorithm on all of the
   // constraints adjacent to these type variables.
   ConnectedComponents cc(*this, typeVars);
-
   return cc.getComponents();
 }