Fix -Wswitch warning introduced by r162231

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162236 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/Option.cpp b/lib/Driver/Option.cpp
index 054f7eb..8a9c601 100644
--- a/lib/Driver/Option.cpp
+++ b/lib/Driver/Option.cpp
@@ -199,6 +199,7 @@
     return new Arg(getUnaliasedOption(), Index - 2,
                    Args.getArgString(Index-2)+getName().size(),
                    Args.getArgString(Index-1));
+  default:
+    llvm_unreachable("Invalid option kind!");
   }
-  llvm_unreachable("Invalid option kind!");
 }