We want the driver-level flag here, else the test passes for the wrong reasons.
See comments on https://reviews.llvm.org/D99901.
// RUN: not %clangxx -nostdinc %s 2>&1 | FileCheck %s
// RUN: not %clangxx -nostdinc++ %s 2>&1 | FileCheck %s
// RUN: not %clangxx -nostdlibinc %s 2>&1 | FileCheck %s
-// RUN: not %clangxx -triple x86_64-unknown-unknown-gnu -fsyntax-only -nostdinc -nostdinc++ %s 2>&1 | FileCheck /dev/null --implicit-check-not=-Wunused-command-line-argument
+// RUN: not %clangxx --target=x86_64-unknown-unknown-gnu -fsyntax-only -nostdinc -nostdinc++ %s 2>&1 | FileCheck /dev/null --implicit-check-not=-Wunused-command-line-argument
// CHECK: file not found
#include <vector>