add a triple

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171808 91177308-0d34-0410-b5e6-96231b3b80d8

test/Misc/ast-dump-attr.cpp

-// RUN: %clang_cc1 -std=c++11 -ast-dump -ast-dump-filter Test %s | FileCheck --strict-whitespace %s
+// RUN: %clang_cc1 -triple x86_64-pc-linux -std=c++11 -ast-dump -ast-dump-filter Test %s | FileCheck --strict-whitespace %s
 
 int TestLocation
 __attribute__((unused));