ASTDumper: Also show TypeAliasType substitution map

Author: slavapestov

lib/AST/ASTDumper.cpp

@@ -4030,12 +4030,10 @@ namespace {
       printCommon("type_alias_type", label);
 
       printFieldQuoted(T->getDecl()->printRef(), "decl");
-      if (auto underlying = T->getSinglyDesugaredType()) {
-        printRec(underlying, "underlying");
-      } else {
-        // This can't actually happen
-        printFlag("unresolved_underlying");
-      }
+      printRec(T->getSinglyDesugaredType(), "underlying");
+
+      if (auto subs = T->getSubstitutionMap())
+        printRec(subs, "substitutions");
 
       if (T->getParent())
         printRec(T->getParent(), "parent");