Silence compiler warning.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@144386 91177308-0d34-0410-b5e6-96231b3b80d8

tools/c-index-test/c-index-test.c

@@ -1617,6 +1617,7 @@ static const char *getEntityKindString(CXIdxEntityKind kind) {
   case CXIdxEntity_Union: return "union";
   case CXIdxEntity_CXXClass: return "c++-class";
   }
+  return "<unknown>";
 }
 
 static void printEntityInfo(const char *cb,