Implement enough of the 'auto' keyword so we can claim to support N2546.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@74307 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Parse/DeclSpec.cpp b/lib/Parse/DeclSpec.cpp
index d8c6986..8b3b285 100644
--- a/lib/Parse/DeclSpec.cpp
+++ b/lib/Parse/DeclSpec.cpp
@@ -173,6 +173,7 @@
   case DeclSpec::TST_typename:    return "type-name";
   case DeclSpec::TST_typeofType:
   case DeclSpec::TST_typeofExpr:  return "typeof";
+  case DeclSpec::TST_auto:       return "auto";
   }
 }