Silencing the warning from r189605 in a more conformant manner.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189606 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/Consumed.cpp b/lib/Analysis/Consumed.cpp
index b004083..745840d 100644
--- a/lib/Analysis/Consumed.cpp
+++ b/lib/Analysis/Consumed.cpp
@@ -74,9 +74,9 @@
     return true;
   case CS_None:
   case CS_Unknown:
-  default:
     return false;
   }
+  llvm_unreachable("invalid enum");
 }
 
 static bool isTestingFunction(const FunctionDecl *FunDecl) {