Clang is not a complete implementation without a library, right? Whoever puts Clang together with a library becomes an integrator who provides a language implementation. It&#x27;s up to that integrator to ensure that the result conforms.<p>Clang could be also used &quot;freestanding&quot;. Then the user might be informed: please supply your own memcpy function with such and such characteristics, since generated code needs it.<p>If those characteristics are just those described in ISO C, but the compiler needs something more, then that&#x27;s a problem between clang and the user.