Add 'not' to commands that are expected to fail.

This is at least good documentation, but also opens the possibility of
using pipefail.

llvm-svn: 185652
diff --git a/clang/test/FixIt/fixit-vexing-parse.cpp b/clang/test/FixIt/fixit-vexing-parse.cpp
index dd0f873..79d8cad 100644
--- a/clang/test/FixIt/fixit-vexing-parse.cpp
+++ b/clang/test/FixIt/fixit-vexing-parse.cpp
@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -verify -x c++ %s
-// RUN: %clang_cc1 -fdiagnostics-parseable-fixits -x c++ %s 2>&1 | FileCheck %s
+// RUN: not %clang_cc1 -fdiagnostics-parseable-fixits -x c++ %s 2>&1 | FileCheck %s
 
 struct S {
   int n;