Add a triple to this test to make buildbots happier.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@278647 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGenCXX/cxx1z-decomposition.cpp

-// RUN: %clang_cc1 -std=c++1z -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -std=c++1z -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
 
 namespace std {
   using size_t = decltype(sizeof(0));