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/CodeGen/Mangle.cpp b/lib/CodeGen/Mangle.cpp
index 24e441a..b5ad5ac 100644
--- a/lib/CodeGen/Mangle.cpp
+++ b/lib/CodeGen/Mangle.cpp
@@ -539,6 +539,9 @@
     assert(false && 
            "Overloaded and dependent types shouldn't get to name mangling");
     break;
+  case BuiltinType::UndeducedAuto:
+    assert(0 && "Should not see undeduced auto here");
+    break;
   }
 }