[IRGen] Collect metadata for empty types fields.

Previously, when the metadata collector only collected for layout, it
was wasteful to visit the empty fields of records.  Now that the field
may require a deinit call, it's necessary to visit it.

rdar://123577998

Author: nate-chandler

lib/IRGen/GenRecord.h

@@ -487,8 +487,6 @@ class RecordTypeInfoImpl : public Base,
   void collectMetadataForOutlining(OutliningMetadataCollector &collector,
                                    SILType T) const override {
     for (auto &field : getFields()) {
-      if (field.isEmpty())
-        continue;
       auto fType = field.getType(collector.IGF.IGM, T);
       field.getTypeInfo().collectMetadataForOutlining(collector, fType);
     }

test/IRGen/moveonly_value_functions.swift

@@ -440,3 +440,26 @@ public func takeOuterMultiPayloadNC_3<T>(_ e: consuming OuterMultiPayloadNC_3<T>
 // CHECK-SAME:        ptr noalias swiftself %0)
 // CHECK:       }
 public func takeOuterMultiPayloadNC_4<T>(_ e: consuming OuterMultiPayloadNC_4<T>) {}
+
+public struct EmptyDeinitingNC_1<Wrapped: ~Copyable>: ~Copyable {
+  deinit {}
+}
+
+public enum SinglePayloadNC_1<Element: Equatable>: ~Copyable {
+  case empty
+  case node(EmptyDeinitingNC_1<Self>, Element)
+}
+// CHECK-LABEL: define{{.*}} @"$s24moveonly_value_functions18EmptyDeinitingNC_1VyAA013SinglePayloadF2_1OyxGG_xtSQRzlWOh"(
+// CHECK-SAME:      ptr %0, 
+// CHECK-SAME:      ptr %Element,
+// CHECK-SAME:      ptr %Element.Equatable)
+// CHECK-SAME:  {
+// CHECK:         [[RESPONSE:%[^,]+]] = call swiftcc %swift.metadata_response @"$s24moveonly_value_functions17SinglePayloadNC_1OMa"(
+//           :        i64 0, 
+// CHECK-SAME:        ptr %Element,
+// CHECK-SAME:        ptr %Element.Equatable)
+// CHECK:         [[METADATA:%[^,]+]] = extractvalue %swift.metadata_response [[RESPONSE]], 0
+// CHECK:         call swiftcc void @"$s24moveonly_value_functions18EmptyDeinitingNC_1VAARiczrlEfD"(
+// CHECK-SAME:        ptr [[METADATA]])
+// CHECK:       }
+