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/CodeGenCXX/const-init.cpp b/clang/test/CodeGenCXX/const-init.cpp
index 201ce8f..05896ff 100644
--- a/clang/test/CodeGenCXX/const-init.cpp
+++ b/clang/test/CodeGenCXX/const-init.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -verify -triple x86_64-apple-darwin -emit-llvm -o - %s | FileCheck %s
+// RUN: not %clang_cc1 -verify -triple x86_64-apple-darwin -emit-llvm -o - %s | FileCheck %s
 
 // CHECK: @a = global i32 10
 int a = 10;