Add missing triple to unit test.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181465 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGenCXX/throw-expressions.cpp

-// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -Wno-unreachable-code -Werror -emit-llvm -o - %s | FileCheck %s
-// expected-no-diagnostics
+// RUN: %clang_cc1 -fcxx-exceptions -fexceptions -Wno-unreachable-code -Werror -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
 
 int val = 42;
 int& test1() {