[Runtime] Include tuple labels when printing the runtime name of a type.

When we started recording labels within the metadata for a tuple type,
we failed to print those labels when rendering the type name from
metadata.

Author: DougGregor

stdlib/public/runtime/Casting.cpp

@@ -285,9 +285,26 @@ static void _buildNameForMetadata(const Metadata *type,
     auto tuple = static_cast<const TupleTypeMetadata *>(type);
     result += "(";
     auto elts = tuple->getElements();
+    const char *labels = tuple->Labels;
     for (unsigned i = 0, e = tuple->NumElements; i < e; ++i) {
       if (i > 0)
         result += ", ";
+
+      // If we have any labels, add the label.
+      if (labels) {
+        // Labels are space-separated.
+        if (const char *space = strchr(labels, ' ')) {
+          if (labels != space) {
+            result.append(labels, space - labels);
+            result += ": ";
+          }
+
+          labels = space + 1;
+        } else {
+          labels = nullptr;
+        }
+      }
+
       _buildNameForMetadata(elts[i].Type, TypeSyntaxLevel::Type, qualified,
                             result);
     }

test/Interpreter/typeof.swift

@@ -51,6 +51,10 @@ class Meltdown : Error {
 
 class GrilledCheese : Meltdown {}
 
+func labeledTuple() -> (x: Int, y: Int, Double) {
+  return (x: 1, y: 1, 3.14159)
+}
+
 // CHECK: Beads?
 classMetatype(type(of: B()))
 // CHECK: Deeds?
@@ -81,3 +85,5 @@ print(boxedExistentialMetatype(Meltdown()))
 print(boxedExistentialMetatype(GrilledCheese()))
 // CHECK: GrilledCheese
 print(boxedExistentialMetatype(GrilledCheese() as Meltdown))
+// CHECK: (x: Int, y: Int, Double)
+print(type(of: labeledTuple()))