RequirementMachine: Generating conformances prefers to delete non-explicit rules

This is a heuristic to ensure that conformance requirements remain in
their original protocol if possible, when the protocol is part of a
connected component consisting of multiple protocols.

lib/AST/RequirementMachine/RequirementMachineRequests.cpp

@@ -200,6 +200,11 @@ RequirementMachine::computeMinimalRequirements() {
   assert(Protos.size() > 0);
   System.minimizeRewriteSystem();
 
+  if (Dump) {
+    llvm::dbgs() << "Minimized rewrite system:\n";
+    dump(llvm::dbgs());
+  }
+
   auto rules = System.getMinimizedRules(Protos);
 
   // Note that we build 'result' by iterating over 'Protos' rather than