Force an unknown target for the default case to make it work.

[filcab]

Summary

This test was failing if LLVM_DEFAULT_TARGET_TRIPLE=x86_64-scei-ps4 due to
its behavior for exceptions.
Force an --unknown triple for the default case.

[chandlerc]

Looks good with a less overly specific comment (see below)

test/Driver/clang-exception-flags.cpp

1–3

I would just say that the default behavior of exception handling in target specific.

test/Driver/clang-exception-flags.cpp

-// RUN: %clang -### %s 2>&1 | FileCheck %s -check-prefix=DEFAULT
+// We have to force the target to unknown for the default, since clang
+// might have been built with LLVM_DEFAULT_TARGET_TRIPLE=x86_64-scei-ps4,
+// which defaults to -fno-exceptions.
+// RUN: %clang -### -target unknown %s 2>&1 | FileCheck %s -check-prefix=DEFAULT
 // DEFAULT: "-cc1" {{.*}} "-fcxx-exceptions" "-fexceptions"
 //
 // RUN: %clang -### -fexceptions %s 2>&1 | FileCheck %s -check-prefix=ON1
 // ON1: "-cc1" {{.*}} "-fcxx-exceptions" "-fexceptions"
 //
 // RUN: %clang -### -fno-exceptions -fcxx-exceptions %s 2>&1 | FileCheck %s -check-prefix=ON2
 // ON2: "-cc1" {{.*}} "-fcxx-exceptions" "-fexceptions"
 //