On 22 Apr 2017, at 23:05, Ken Cunningham <ken.cunningham.webuse at gmail.com> wrote: > because cxx_stdlib will equal libc++ and therefore this test (which would lead to the code that does the whitelisting) will fail. Bear with me — what I actually had in mind was, since we have LibcxxOnOlderSystems instructions, why doesn't it explicitly test against libc++?