Don't actually execute gcc during testing.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@154005 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Driver/apple-kext-i386.cpp b/test/Driver/apple-kext-i386.cpp
index 6c53607..a09d6a6 100644
--- a/test/Driver/apple-kext-i386.cpp
+++ b/test/Driver/apple-kext-i386.cpp
@@ -43,5 +43,9 @@
 
 // Check that --serialize-diagnostics does not cause an "argument unused" error.
 // RUN: %clang -target i386-apple-darwin10 \
-// RUN:   -Werror -Wall -Wno-comment -fapple-kext \
-// RUN:   --serialize-diagnostics %t.dia -c %s
+// RUN:   -Werror -Wall -Wno-comment -fapple-kext -### \
+// RUN:   --serialize-diagnostics %t.dia -c %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=CHECK-UNUSED %s
+
+// CHECK-UNUSED-NOT: argument unused
+// CHECK-UNUSED: cc1plus